Wireless communication device, wireless communication terminal and wireless communication method

ABSTRACT

According to one embodiment, a wireless communication device, includes a receiver configured to receive a first field, receive at least one of a plurality of second fields having been multiplexed and transmitted, and decode the one of the second fields to obtain a frame in a case where first information identifying the wireless communication device is not set in the first field, and a controller configured to suppress access to a wireless medium during a period indicated by a value set in the frame.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/706,572, filed on Sep. 15, 2017, which is a Continuation ofInternational Application No. PCT/JP2016/063507, filed on Apr. 28, 2016,the entire contents of all of the above applications are herebyincorporated by reference.

FIELD

Embodiments of the present invention relate to a wireless communicationdevice, wireless communication terminal and wireless communicationmethod.

BACKGROUND

A communication scheme that simultaneously performs transmissiondestined for multiple wireless communication terminals (hereinafter,terminals) or reception from the multiple terminals and is called OFDMA(Orthogonal Frequency Division Multiple Access) has been known. OFDMAthat allocates one or more subcarriers as a resource block to a terminaland simultaneously performs transmission to multiple terminals orreception from the multiple terminals on a resource block basis isspecifically called a resource-block-based OFDMA in some cases.Simultaneous transmission from a base station to multiple terminalscorrespond to downlink OFDMA transmission. Simultaneous transmissionfrom the multiple terminals to the base station corresponds to uplinkOFDMA transmission.

In a case where communication is executed through resource-block-basedOFDMA in a wireless LAN system in conformity with IEEE 802.11 standardusing CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance),presence of terminals that are not targets of OFDMA in the system isrequired to be considered. The terminals that are not OFDMA targets areterminals that do not serve as the targets of OFDMA executed in thiscase.

When OFDMA communication is performed in an environment where a terminalnot serving as an OFDMA target (non-target terminal) resides, thenon-target terminal does not successfully receive frames (morespecifically, physical packets including frames) that are exchanged inOFDMA. Consequently, an error is detected in the physical layer or MAClayer. Accordingly, in the next access to a wireless medium, an EIFS(Extended Interframe Space) period is set as a fixed period of time toperform carrier sensing on the MAC layer. The EIFS period is longer thanDIFS/AIFS [AC] which is a fixed period of time used in carrier sensingperformed in normal medium access. Consequently, unfairness occursbetween non-target terminals and the other terminals (e.g., terminalsand a base station that execute OFDMA communication) in access rightobtaining opportunities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a wireless communication deviceaccording to an embodiment of the present invention;

FIG. 2 is a diagram for illustrating OFDMA communication and resourceblock allocation;

FIG. 3 is a diagram showing a wireless communication group formed of abase station and multiple terminals;

FIG. 4 is a diagram for illustrating unfairness in accessing a wirelessmedium and can be caused by OFDMA communication;

FIGS. 5A and 5B each is a diagram showing a schematic format example ofa physical packet;

FIG. 6 is a diagram showing a basic format example of a MAC frame;

FIGS. 7A and 7B each is a diagram schematically showing a carrier senseperiod;

FIG. 8 is a diagram showing an example of an operation sequenceaccording to a first embodiment;

FIG. 9 is a diagram showing another example of the operation sequenceaccording to the first embodiment;

FIG. 10 is a flowchart showing an operation of a base station accordingto the first embodiment;

FIG. 11 is a flowchart showing an operation of a terminal according tothe first embodiment;

FIG. 12 is a diagram showing a first example of an operation sequenceaccording to a second embodiment;

FIG. 13 is a diagram showing a second example of the operation sequenceaccording to the second embodiment;

FIG. 14 is a diagram showing a flowchart of an operation of the basestation corresponding to the operation sequence example shown in FIG. 13;

FIG. 15 is a diagram showing a first example of an operation sequenceaccording to a third embodiment;

FIG. 16 is a diagram showing a flowchart of an operation of the basestation corresponding to the operation sequence example shown in FIG. 15;

FIG. 17 is a diagram showing a second example of the operation sequenceaccording to the third embodiment;

FIG. 18 is a diagram showing a third example of the operation sequenceaccording to the third embodiment;

FIG. 19 is a diagram showing a flowchart of an operation of the basestation corresponding to the operation sequence example shown in FIG. 18;

FIG. 20 is a diagram for illustrating unfairness in accessing a wirelessmedium and can be caused by MU-MIMO communication;

FIG. 21 is a diagram showing a first example of an operation sequenceaccording to a fourth embodiment;

FIG. 22 is a diagram showing a second example of an operation sequenceaccording to the fourth embodiment;

FIG. 23 is a diagram showing a third example of the operation sequenceaccording to the fourth embodiment;

FIG. 24 is a diagram showing a fifth example of the operation sequenceaccording to the fourth embodiment;

FIG. 25 is a diagram showing a sixth example of the operation sequenceaccording to the fourth embodiment;

FIG. 26 is a diagram showing a seventh example of the operation sequenceaccording to the fourth embodiment;

FIG. 27 is a functional block diagram of a base station or a terminalaccording to the fifth embodiment;

FIG. 28 shows an overall configuration example of a terminal or a basestation according to a sixth embodiment;

FIG. 29 is a diagram showing a hardware configuration example of awireless communication device mounted on a base station or a terminalaccording to the sixth embodiment;

FIGS. 30A and 30B each is a perspective view of a wireless communicationterminal according to a seventh embodiment;

FIG. 31 is a diagram showing a memory card according to the seventhembodiment; and

FIG. 32 is a diagram showing an example of frame exchange in acontention period.

DETAILED DESCRIPTION

According to one embodiment, a wireless communication device, includes areceiver configured to receive a first field, receive at least one of aplurality of second fields having been multiplexed and transmitted, anddecode the one of the second fields to obtain a frame in a case wherefirst information identifying the wireless communication device is notset in the first field, and a controller configured to suppress accessto a wireless medium during a period indicated by a value set in theframe.

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The entire contents of IEEE Std 802.11-2012and IEEE Std 802.11ac-2013, known as the wireless LAN standard and IEEE802.11-15/0132r15 which is Specification Framework Document directed toIEEE Std 802.11ax as a next generation wireless LAN standard are hereinincorporated by reference in the present specification.

First Embodiment

FIG. 1 shows a functional block diagram of a wireless communicationdevice according to a first embodiment. The wireless communicationdevice can be implemented in a wireless communication base station(hereinafter, a base station), or a wireless communication terminal(hereinafter, a terminal) that communicates with the wirelesscommunication base station. The base station is different from theterminal in that the base station has a relay function but, in otherpoints, has communication functions basically analogous to those of theterminal. Consequently, the base station can be regarded as one mode ofthe terminal. When a wireless communication terminal or a terminal ismentioned in the following explanations, it may also refer to a basestation as long as the terminal and the base station need not to beparticularly discriminated from each other.

This embodiment assumes that the base station performsresource-block-based OFDMA (Orthogonal Frequency Division MultipleAccess) communication that allocates, to the terminals, resource blocks(which may also be called subchannels, resource units or frequencyblocks) each including one or more continuous subcarriers in acontinuous frequency domain, and performs simultaneous transmissiondestined for the multiple terminals or simultaneous reception from themultiple terminals. The transmission from the base station to themultiple terminals is corresponded to downlink OFDMA transmission. Thetransmission from the multiple terminals to the base station iscorresponded to uplink OFDMA transmission.

FIG. 2 shows situations where multiple channels are arranged in afrequency domain. A guard band is provided between channels. Thebandwidth of one channel is, for example, 20 MHz. It is assumed that thecontinuous band of one channel (here, channel M) thereamong is used forOFDMA communication. In the continuous band of channel M (e.g., 20 MHzwidth band), multiple (e.g., 52 in a case of 20 MHz band) subcarriersorthogonal to each other are arranged. On the basis of thesesubcarriers, the resource blocks that adopt one or more continuoussubcarriers as a unit are allocated to terminal 1, terminal 2, . . . ,terminal K (K is an integer of two or larger). The resource blocks havethe same bandwidth (or the same number of subcarriers) with respect toeach other. Alternatively, the individual resource blocks may be allowedto have bandwidths (or the numbers of subcarriers) different from eachother. The number of resource blocks allocated to each terminal isconfigured such that one resource block is for one terminal in theexample of FIG. 2 . Alternatively, multiple resource blocks may beallocated to one terminal. The number of allocated resource blocks maybe different among individual terminals. In a case where the resourceblock includes multiple subcarriers, the arrangement of the subcarriersincluded in the resource block may be continuous or discontinuous.Discontinuously arranged multiple subcarriers may be allocated as aresource block to one wireless terminal.

In the example in FIG. 2 , at least one subcarrier is arranged as aguard subcarrier between the resource blocks allocated to the respectiveterminals. The number of guard subcarriers arranged between the resourceblocks may be defined in a system or a specification or in any manner.The arrangement of the guard subcarrier between the resource blocks isnot necessary. Alternatively, arrangement with no guard subcarrierbetween the resource blocks may be allowed.

The number of channels used for OFDMA communication is not limited toone. Alternatively, OFDMA communication can be performed using two ormore channels. In this case, the resource blocks may be allocated ineach channel independently in a channel-by-channel basis. In this case,multiple resource blocks belonging to different channels may be allowedto be allocated to one terminal. The resource blocks are not necessarilyallocated in the independent manner for each channel. Alternatively, acontinuous frequency domain made up of channels coupled to each othermay be defined, the resource blocks may be allocated in the combinedfrequency domain. For example, two channels adjacent to each other inview of frequency may be coupled to define a 40-MHz frequency domain,and the resource blocks may be allocated on the basis of subcarriersorthogonal to each other in the 40-MHz frequency domain. Likewise, four20 MHz width channels may be combined to define an 80-MHz frequencydomain, or eight channels may be combined to define 160-MHz frequencydomain. In this case, the resource blocks may be allocated on the basisof the subcarriers orthogonal to each other in each frequency domain.

A terminal according to this embodiment is successful in carrying outreception and decoding (including decoding of error correcting code anddemodulation, etc.) of a physical packet of at least the referencechannel width (20 MHz channel width if IEEE 802.11a/b/g/n/ac standardcompliant terminal is regarded as a legacy terminal) at the legacyterminal that is to be backward compatible. In this case, with regard tothe carrier sensing, it is carried out in a unit of a channel. It mayencompass both physical carrier sensing associated with busy/idle of CCA(Clear Channel Assessment) and virtual carrier sensing based on mediumreservation time indicated in the received frame. As in the case of thelatter, a scheme for virtually determining that a medium is in the busystate, or the term during which the medium is virtually regarded asbeing in the busy state is called a Network Allocation Vector (NAV). Thecarrier sense information based on CCA or a NAV carried out in a unit ofa channel may be universally applied to all the resource blocks withinthe channel. For example, to resource blocks belonging to a channel thathas carrier sense information indicating an idle state, the carriersense information on the channel may be commonly applied, and theresource blocks may be regarded as an idle state and thus be processed.The terminal according to this embodiment is not limited to the mode ofperforming carrier sensing in units of channels. Alternatively, if aterminal is implemented with a scheme where the terminal performscarrier sensing in units of resource blocks, the carrier sensing inunits of resource blocks (in both physical and virtual manners) may beallowed.

This embodiment assumes that resource-block-based OFDMA communication isperformed between the base station and the multiple terminals, asdescribed before. The scheme is not limited to the resource-block basedone. Alternatively, channel-based OFDMA communication may be allowed. Inparticular, OFDMA in this case is sometimes called channel-based OFDMAor MU-MC (Multi-User Multi-Channel). In MU-MC, the base stationallocates multiple channels to multiple terminals, and performssimultaneous transmission destined for the multiple terminals orsimultaneous reception from the multiple terminals simultaneously usingthe multiple channels. The following description of the embodiment onresource-block-based OFDMA may be read with required replacement inconformity with channel-based OFDMA, for example, in a manner where theresource block is replaced with the channel, thereby enabling anembodiment of channel-based OFDMA to be achieved.

In the following description, a terminal that has a capability ofexecuting resource-block-based OFDMA communication is called an OFDMAcompatible terminal, and a terminal that does not have this capabilityis called a legacy terminal, in some cases. In a case where thecapability of executing OFDMA communication is switchable between anenabled state (Enable) and a disabled state (Disable), a terminal wherethe capability is switched to the enabled state may be regarded as anOFDMA compatible terminal. The terminal designated as the base stationfor OFDMA communication this time among the OFDMA compatible terminalscorresponds to an OFDMA target terminal. The terminals that are notdesignated as the base station for OFDMA communication this time aresometimes called OFDMA non-target terminals.

As illustrated in FIG. 1 , a wireless communication device incorporatedin a terminal (which may be either a terminal of non-base station or thebase station) includes upper layer processor 90, MAC processor 10,physical (PHY) processor 50, MAC/PHY manager 60, analog processor 70(analog processors 1 to N), and antenna 80 (antennas 1 to N), where Nrepresents an integer equal to or larger than 1. In the figure, the Nanalog processors and the N antennas are connected in pairs with eachother, but the configuration is not limited to the illustrated one. Forexample, one analog processor and two or more antennas may be connectedto this analog processor in a shared manner.

MAC processor 10, MAC/PHY manager 60 and PHY processor 50 eachcorresponds to one mode of a communication processing device or abaseband integrated circuit that performs a process pertaining tocommunication with another terminal (including the base station). Analogprocessor 70 corresponds, for example, to a wireless communicator or aradio frequency (RF) integrated circuit that transmits and receivessignals via antenna 80. The integrated circuit for wirelesscommunication in accordance with this embodiment may include at leastthe former of the baseband integrated circuit (communication processingdevice) and the RF integrated circuit. The functions of thecommunication processing device or the baseband integrated circuit maybe performed by software (programs) that runs on a processor such as aCPU or may be performed by hardware, or may be performed by both of thesoftware and the hardware. The software may be stored in a storagemedium such as a memory including a ROM, a RAM, etc., a hard disk, or anSSD and read therefrom to be executed. The memory may be a volatilememory such as a DRAM, or a non-volatile memory such as a NAND or anMRAM.

Upper layer processor 90 is configured to carry out processing for theMedium Access Control (MAC) layer associated with the upper layer orlayers. Upper layer processor 90 can exchange signals with MAC processor10. As the upper layer, TCP/IP, UDP/IP, and the application layer upperthan these two protocols may be mentioned as typical examples but thisembodiment is not limited to them. Upper layer processor 90 may includea buffer for exchanging data between the MAC layer and the upper layeror layers. It may also be considered that it may be connectable to awired infrastructure via upper layer processor 90. The buffer may be amemory, an SSD, a hard disk or the like. In the case where the buffer isa memory, the memory may be a volatile memory, such as DRAM, or anonvolatile memory, such as NAND or MRAM.

MAC processor 10 is configured to carry out processing for the MAClayer. As described before, MAC processor 10 can exchange signals withupper layer processor 90. Further, MAC processor 10 can exchange signalswith PHY processor 50. MAC processor 10 includes MAC common processor20, transmission processor 30, and reception processor 40.

MAC common processor 20 is configured to carry out common processing fortransmission and reception in the MAC layer. MAC common processor 20 isconnected to and exchanges signals with upper layer processor 90,transmission processor 30, reception processor 40, and MAC/PHY manager60.

Transmission processor 30 and reception processor 40 are connected toeach other. Also, transmission processor 30 and reception processor 40are each connected to MAC common processor 20 and PHY processor 50.Transmission processor 30 is configured to carry out transmissionprocessing in the MAC layer. Reception processor 40 is configured tocarry out reception processing in the MAC layer.

PHY processor 50 is configured to carry out processing for a physicallayer (PHY layer). As described before, PHY processor 50 can exchangesignals with MAC processor 10. PHY processor 50 is connected via analogprocessor 70 to antenna 80.

MAC/PHY manager 60 is connected to upper layer processor 90, MACprocessor 10 (more specifically, MAC common processor 20), and PHYprocessor 50. MAC/PHY manager 60 is configured to manage MAC operationand PHY operation in the wireless communication device.

Analog processor 70 includes an analog-to-digital and digital-to-analog(AD/DA) converter and a radio frequency (RF) circuit. Analog processor70 is configured to convert a digital signal from PHY processor 50 intoan analog signal having a desired frequency and transmit it from antenna80, or convert a high-frequency analog signal received from antenna 80into a digital signal. It is considered here that although AD/DAconversion is carried out by analog processor 70, another configurationis also possible according to which PHY processor 50 has the AD/DAconversion function.

The wireless communication device in accordance with this embodiment hasits constituent element (i.e., incorporates) antenna 80 in one singlechip and thereby makes it possible to reduce the mounting area ofantenna 80. Further, in the wireless communication device in accordancewith this embodiment, as illustrated in FIG. 1 , transmission processor30 and reception processor 40 shares N antennas 80. By virtue of sharingN antennas 80 by transmission processor 30 and reception processor 40,it is made possible to reduce the size of the wireless communicationdevice of FIG. 1 . It is considered here that the wireless communicationdevice in accordance with this embodiment may have a configurationdifferent than the one depicted by way of example in FIG. 1 .

In reception of a signal from a wireless medium, analog processor 70converts an analog signal received by antenna 80 into a baseband signalthat can be processed by PHY processor 50, and further converts thebaseband signal into a digital signal. PHY processor 50 is configured toreceive a digital received signal from analog processor 70 and detectits reception level. The detected reception level is compared with thecarrier sense level (threshold). When the reception level is equal to orlarger than the carrier sense level, PHY processor 50 outputs a signalindicative of the determination result that the medium (CCA: ClearChannel Assessment) is in the busy state to MAC processor 10 (receptionprocessor 40 to be more precise). When the reception level is less thanthe carrier sense level, PHY processor 50 outputs a signal indicative ofthe determination result that the medium (CCA) is in the idle state toMAC processor 10 (reception processor 40 to be more precise).

PHY processor 50 applies a decoding (including decoding, demodulatingand the like of an error correction code) process and a process ofremoving the preamble and the PHY header to the received signal, andextracts the payload. According to IEEE 802.11 standard, this payload iscalled physical layer convergence procedure (PLCP) service data unit(PSDU) on the PHY side. PHY processor 50 delivers the extracted payloadto reception processor 40, and reception processor 40 handles it as aMAC frame. According to IEEE 802.11 standard, this MAC frame is calledmedium access control (MAC) protocol data unit (MPDU). In addition, PHYprocessor 50, when it started to receive the reception signal, notifiesthe fact of having started reception of the reception frame to receptionprocessor 40, and, when it completed the reception of the receptionsignal, notifies the fact of having completed the reception to receptionprocessor 40. Also, PHY processor 50, when the reception signal has beendecoded successfully as the physical packet (PHY packet) (when it doesnot detect an error), notifies the completion of the reception of thereception signal and delivers a signal indicative of the fact that themedium is in the idle state to reception processor 40. PHY processor 50,when it detected an error in the reception signal, notifies the factthat the error has been detected with an appropriate error code inaccordance with the error type to reception processor 40. Also, PHYprocessor 50, at the timing at which the medium has been determined toenter the idle state, notifies a signal indicative of the fact that themedium is in the idle state to reception processor 40.

MAC common processor 20 performs intermediary processing for delivery oftransmission data from upper layer processor 90 to transmissionprocessor 30 and for delivery of reception data from reception processor40 to upper layer processor 90. According to IEEE 802.11 standard, thedata in this MAC data frame is called medium access control (MAC)service data unit (MSDU). Also, MAC common processor 20 receivesinstructions from MAC/PHY manager 60 and then converts the instructioninto ones appropriate for each form of instructions for transmissionprocessor 30 and reception processor 40 and outputs the convertedinstructions to these units.

MAC/PHY manager 60 corresponds, for example, to station managemententity (SME) in IEEE 802.11 standard. In that case, the interfacebetween MAC/PHY manager 60 and MAC common processor 20 corresponds toMAC subLayer management entity service access point (MLME SAP) in IEEE802.11 standard, and the interface between MAC/PHY manager 60 and PHYprocessor 50 corresponds to physical layer management entity serviceaccess point (PLME SAP) in IEEE 802.11 wireless local area network(LAN).

It is considered here that although MAC/PHY manager 60 in FIG. 1 isillustrated on the assumption that the functional unit for the MACmanagement and the functional unit for the PHY management are configuredto be integral with each other, these units may be separatelyimplemented.

MAC/PHY manager 60 holds a management information base (MIB). The MIBholds various pieces of information, such as the capabilities of the ownterminal, and the validities of various functions. For example,information on whether the own terminal is the OFDMA compatible terminalor not and on/off information of the capability of executing OFDMA in acase of the OFDMA compatible terminal may also be held. A memory forholding and managing the MIB may be included in MAC/PHY manager 60, orseparately provided without being included in MAC/PHY manager 60. In acase where the memory for holding and managing the MIB is separatelyprovided besides MAC/PHY manager 60, MAC/PHY manager 60 can refer to theother memory and rewrite rewritable parameters in the memory. The memorymay be a volatile memory, such as DRAM, or a nonvolatile memory, such asNAND or MRAM. Instead of the memory, a storage device, such as an SSD ora hard disk, may be adopted. The base station can receive suchinformation at other non-base station terminals, by means ofnotification from the terminals which are non-base stations. In thiscase, MAC/PHY manager 60 can refer to and rewrite information pertainingto other terminals. A memory for storing information pertaining to theother terminals may be held and managed separately from the MIB. In thiscase, it is configured so that MAC/PHY manager 60 or MAC commonprocessor 20 can refer to or rewrite the other memory. For OFDMAcommunication, MAC/PHY manager 60 of the base station may also have agrouping function that selects terminals to which resource blocks forOFDMA communication are to be simultaneously allocated (i.e., selectsterminals serving as targets of OFDMA at this time) on the basis ofvarious pieces of information pertaining to the terminals serving asnon-base stations or a request issued by the terminal. MAC/PHY manager60 or MAC processor 10 may manage the transmission rate to be applied tothe MAC frame and physical header to be transmitted. MAC/PHY manager 60of the base station may define a supported rate set that is a rate setsupported by the base station. The supported rate set may include a ratenecessarily supported by the terminals connected to the own station, andoptional rates.

MAC processor 10 is configured to handle three types of MAC frames,i.e., a data frame, a control frame, and a management frame, and carryout various processing procedures defined in the MAC layer. Here, thethree types of MAC frames are described.

The management frame is for use in management of communication link withanother terminal. As the management frame, for example, a Beacon framemay be mentioned. The Beacon frame notifies attribute andsynchronization information of a group to form a wireless communicationgroup which is a Basic Service Set (BSS) in IEEE 802.11 standard. Also,a frame exchanged for authentication or establishing the communicationlink may also be mentioned. It is considered here that a state where acertain terminal completed exchange of information necessary forestablishing a wireless communication with another terminal is expressedhere as (the state where) the communication link is established.Required information exchange includes, for example, notification on afunction supported by the own terminal (e.g., OFDMA scheme supported,and various capabilities described later, etc.), negotiations pertainingto scheme setting and the like. The management frame is generated on thebasis of the instruction received by transmission processor 30 fromMAC/PHY manager 60 via MAC common processor 20.

With regard to the management frame, transmission processor 30 includesa notifier which notifies various pieces of information to otherterminals by the management frame. A terminal that is not a base stationmay notify information on the terminal itself to the base station byputting in the management frame information regarding such as whether itis an OFDMA-compliant a terminal, IEEE802.11n compliant terminal orIEEE802.11ac compliant terminal. As for this management frame, forexample, Association Request frame used in the association process orReassociation Request frame used in the reassociation process may bementioned. The association process and the reassociation process arekinds of steps taken for authentication between the terminal and thebase station. The notifier of the base station may notify information onOFDMA supportability to the non-base station through the managementframe. The management frame used for this may be, for example, a beaconframe, or a probe response frame that is a response to a probe requestframe transmitted from the non-base station terminal. The base stationmay have the function of grouping the terminals connected to the ownstation and the notifier of the base station may notify the assignedgroup IDs to the terminals through the management frames. The managementframe may be, for example, a group ID management fame. The group ID maybe a group ID defined in IEEE Std 802.11ac-2013. In OFDMA communicationin the unit of the group, the base station may notify informationrequired for identifying the resource blocks used by the terminalsbelonging to the group, through any management frame.

Reception processor 40 has a receiver that receives various types ofinformation via the management frame from other terminals. For example,the receiver of the base station may receive information on whetherOFDMA communication is supported or not from the terminal serving as thenon-base station. The terminal may also receive information on a channelwidth supported by each terminal (an available largest channel width) ina case of a legacy terminal (IEEE 802.11n compliant terminal or IEEE802.11ac compliant terminal). The receiver of the terminal may receiveinformation on whether the base station supports OFDMA communication ornot.

The examples of the information to be transmitted and received via themanagement frame as described before are merely examples and variousother types of information can be transmitted and received via themanagement frame between terminals (including the base station). Forexample, the OFDMA compatible terminal may select the resource block orthe channel or both of them that this terminal wishes to use for OFDMAcommunication, from among the non-interfering channels ornon-interfering resource blocks in carrier sensing or both of them. Theterminal may notify information pertaining to the selected resourceblock or channel or both of them to the base station. In this case, thebase station may allocate the resource block for OFDMA communication toeach OFDMA compatible terminal on the basis of this information. Thechannel(s) used for OFDMA communication may be all the channels usablefor wireless communication system or some (one or multiple) channel(s).

The data frame is for use in transmission of data to another terminal ina state where the communication link is established with the otherterminal. For example, data is generated in the terminal by an operationof an application by a user, and the data is carried by the data frame.More specifically, the generated data is passed from upper layerprocessor 90 to transmission processor 30 via MAC common processor 20.Transmission processor 30 stores the data into a frame body field, andadds a MAC header to generate a data frame. PHY processor 50 then adds aphysical header to the data frame to generate a physical packet. Thephysical packet is transmitted through analog processor 70 and antenna80. Upon receipt of the physical packet, PHY processor 50 performs aprocess on the physical layer on the basis of the physical header toextract the MAC frame (here, the data frame), and passes the data frameto reception processor 40. When reception processor 40 receives the dataframe (grasps that the received MAC frame is the data frame), thisprocessor extracts the information on the frame body field as data, andpasses the extracted data to upper processor 90 via MAC common processor20. As a result, operations occur on applications such as writing,reproduction, and the like of the data.

The control frame is utilized to control in transmission and reception(exchange) of the management frame and the data frame to/from (with) theother wireless communication device. As the control frame, for example,an RTS (Request to Send) frame, a CTS (Clear to Send) frame may bementioned which are exchanged with the other wireless communicationdevice to make a reservation of the wireless medium prior to startingexchange of the management frame and the data frame. Other controlframes include acknowledgement response frames for acknowledgement ofreceived management frames and data frames. Examples of theacknowledgement response frames include an ACK (Acknowledgement) frameand a BA (BlockACK) frame. A CTS frame can be regarded as a frame thatindicates an acknowledgement response because the CTS frame istransmitted as a response to an RTS frame. A CF-End frame is also one ofthe control frames. The CF-End frame is a frame that announces the endof CFP (Contention Free Period), that is, a frame for permitting accessto the wireless medium. These control frames are generated bytransmission processor 30. As for the control frame (the CTS frame, theACK frame, the BA frame or the like) transmitted as a response to thereceived MAC frame, reception processor 40 determines the necessity oftransmission of the response frame (control frame), and outputsinformation (the information to be set for the type, the RA field etc.of the control frame) required to generate the frame, together with atransmission instruction, to transmission processor 30. Transmissionprocessor 30 generates an appropriate control frame on the basis of theinformation necessary for generation of the frame and the transmissioninstruction.

When a MAC frame is transmitted on the basis of CSMA/CA (Carrier SenseMultiple Access with Collision Avoidance), MAC processor 10 needs toacquire the access right (transmission right) on the wireless medium.Transmission processor 30, on the basis of carrier sense informationfrom reception processor 40, measures transmission timing. Transmissionprocessor 30, in accordance with the transmission timing, gives thetransmission instruction to PHY processor 50, and further delivers theMAC frame thereto. In addition to the transmission instruction,transmission processor 30 may instruct a modulation scheme and a codingscheme to be used in the transmission. In addition to them, transmissionprocessor 30 may provide an instruction regarding the transmissionpower. When MAC processor 10, after having acquired the access right(transmission right), obtained the period of time during which themedium can be occupied (Transmission Opportunity; TXOP), then MACprocessor 10 is allowed to continuously exchange the MAC frames withother wireless communication devices although there is some limitationbased on such as the QoS (Quality of Service) attribute. The TXOP isacquired, for example, when the wireless communication device transmitsa predetermined frame (for example, an RTS frame) on the basis ofCSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) andsuccessfully receives a response frame (for example, a CTS frame) fromanother wireless communication device. When this predetermined frame isreceived by the other wireless communication device, the other wirelesscommunication device transmits the above response frame after the elapseof the minimum frame interval (Short InterFrame Space; SIFS). A methodof obtaining TXOP using no RTS frame may be, for example, a case where adata frame for requesting transmission of an acknowledgement responseframe directly in unicast (the data frame may be a frame having a formwhere frames are aggregated, or a frame having a form where payloads areaggregated, as described later) or a management frame is transmitted,and an acknowledgement response frame (an ACK frame or a BlockACK frame)is correctly received in response thereto. Alternatively, in a case oftransmission of a frame that does not request another wirelesscommunication device to transmit an acknowledgement response frame andhas a Duration/ID field (hereinafter Duration field) where duration morethan a period required to transmit this frame has been set, it can beinterpreted that TXOP having duration described in the Duration fieldafter the stage of transmission of this frame is obtained.

Reception processor 40 is configured to manage the carrier senseinformation as described before. The carrier sense information ismanaged in units of a channel. This carrier sense information includesboth physical carrier sense information regarding busy/idle states ofthe medium (CCA) input from PHY processor 50 and virtual carrier senseinformation on the basis of the medium reservation time described in thereceived frame. If either one of these carrier sense information piecesindicates the busy state, then the medium is regarded as being in thebusy state in which transmission is prohibited. It is considered herethat in IEEE 802.11 standard, the medium reservation time is describedin the Duration field of the MAC header. MAC processor 10, when havingreceived a MAC frame that is addressed to other wireless communicationdevices (that is not addressed to the device itself), determines thatthe medium is virtually in the busy state from the end of the physicalpacket including this MAC frame over the medium reservation time. Ascheme of this type for virtually determining that a medium is in thebusy state, or the term during which the medium is virtually regarded asbeing in the busy state is called a Network Allocation Vector (NAV). Themedium reservation period represents the length of duration ofinstructing suppression of access to the wireless medium, that is, thelength of duration of determining of access to the wireless medium.

Here, the data frame may be a frame such that a plurality of MAC frames(i.e., MPDUs or sub-frames) are aggregated with each other or payloadportions of a plurality of MAC frames are aggregated with each other.The former data frame is called an A (Aggregated)-MPDU and the latterdata frame is called an A (Aggregated)-MSDU (MAC service data unit) inIEEE 802.11 standard. In the case of the A-MPDU, a plurality of MPDUsare aggregated with each other within the PSDU. Also, as a MAC frame, inaddition to the data frame, the management frame and the control frameare also eligible for this aggregation. In the case of the A-MSDU, MSDUswhich are a plurality of data payloads are aggregated within the framebody of one MPDU. As for each of A-MPDU and A-MSDU, partitioninformation (length information, etc.) is stored in the data frame sothat the aggregation of multiple MPDUs and the aggregation of multipleMSDUs can be appropriately separated at the receiver terminal. Both ofthe A-MPDU and the A-MSDU may be used in combination. The target ofA-MPDU may be only one MAC frame instead of multiple MAC frames. Also inthis case, the partition information is stored in the data frame. Also,the responses to the plurality of MAC frames are collectivelytransmitted in such a case of the data frame being A-MPDU. For theresponse in this case, the BA (BlockACK) frame is used instead of theACK frame. In the following description and diagrams, the representationof MPDU may sometimes be used. This case also includes not only the caseof the single MAC frame but also the case of A-MPDU or A-MSDU describedbefore.

According to IEEE 802.11 standard, several procedures are defined inmultiple stages to be taken for a terminal that is not the base stationto participate in a BSS (which is called an infrastructure BSS)configured with the base station amongst others and to perform exchangeof data frames within the BSS. For example, there is provided aprocedure called association, according to which an Association Requestframe is transmitted from the terminal that is not the base station tothe base station to which the terminal requests the connection. The basestation, after having transmitted an ACK frame for the associationrequest frame, transmits an Association Response frame which is aresponse to the association request frame.

The terminal stores the capability of the own terminal in an associationrequest frame. Transmission thereof allows the capability of the ownterminal to be notified to the base station. For example, the terminalmay store the channel or resource block or both of them that can besupported by the own terminal, or information for identifying thestandards supported by the own terminal, in the association requestframe, and transmit the frame. This information may also be stored in aframe to be transmitted in procedures called reassociation forreconnection to another base station. In this procedure ofreassociation, a Reassociation Request frame is transmitted to the basestation to which reconnection is requested from the terminal. The basestation, after having transmitted the ACK frame in response to thereassociation request frame, transmits a reassociation response which isa response to the reassociation request frame.

As the management frame, in addition to the association request frameand the reassociation request frame, a beacon frame, a probe responseframe, etc. may be used. The beacon frame is basically transmitted bythe base station, and can store parameter notifying the capability ofthe base station itself along with the parameters indicating theattributes of the BSS. In view of this, as the parameter notifying thecapability of the base station itself, the base station may be adaptedto add the information on whether or not OFDMA is supported by the basestation. Information on the supported rate of the base station may benotified as another parameter. The supported rate may contain amandatory rate and optional rates. The probe response frame is a frametransmitted from a terminal (base station) that transmits the beaconframe in response to a probe request frame received. The probe responseframe is basically for notifying the same content as the beacon frame.Consequently, the base station can notify the capability of the ownstation (whether OFDMA communication is supported or not, the supportedrates, etc.) to the terminal having transmitted the probe response framealso through use of the probe response frame. This notification to theOFDMA compatible terminal allows the terminal to enable the function ofthe OFDMA communication of the own terminal, for example.

The terminal may notify information on the rate feasible by the ownterminal among the supported rates of the base station, as informationto be notified about the own terminal's capability, to the base station.As for the mandatory rate among the supported rates, the terminalconnected to the base station has a capability of executing themandatory rate. In some cases, the base station defines no supportedrate. In such cases, the terminal can execute the mandatory rate setaccording to the type of the physical layer.

If there is a piece of information which is among the pieces ofinformation described before and for which transmission of another pieceof information makes this piece mandatory, the notification can beomitted. For example, in a case where the capability conforming to acertain new standards or specification is defined and conformitytherewith automatically means the OFDMA compatible terminal, it is notnecessarily explicitly notified that the terminal is an OFDMA compatibleterminal.

FIG. 3 shows a wireless communication system according to thisembodiment. This system includes base station (AP: Access Point) 100 andmultiple terminals (STA: STAtions) 1 to 8. Base station 100 andsubordinate terminals 1 to 8 form BSS (Basic Service Set) 1. This systemis a wireless LAN system in conformity with IEEE 802.11 standard thatuses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).The OFDMA compatible terminals and legacy terminals coexist. Forexample, terminals 1 to 6 are the OFDMA compatible terminals, andterminals 7 and 8 are the legacy terminals. Description is hereinaftermade assuming this fact.

In the system in FIG. 3 , in a case of execution of resource-block-basedOFDMA, the equality of medium access opportunity after OFDMAcommunication is required to be considered between the OFDMA non-targetterminals (terminals having not been designated as targets of OFDMAcommunication this time) and the target terminals and the base station.Upon receipt of frames (more specifically, physical packets containingframes) simultaneously transmitted from the base station or otherterminals in OFDMA, the non-target terminal typically performs decodingonly up to the common preamble of the header of the physical packet(e.g., a case where it is determined that the physical packet does notcontain the frame destined for the own terminal on the basis of thecontent of the common preamble). In this case, an error is detected onthe physical layer, and the error is notified to the MAC layer via theSAP (Service Access Point). Accordingly, on the MAC layer, EIFS(Extended Interframe Space) period is set as a certain duration ofcarrier sensing before backoff, at the next medium access. The EIFSperiod is longer than the certain period (DIFS/AIFS[AC]) of carriersensing performed at normal medium access. Consequently, unfairnessoccurs between the non-target terminals that set the EIFS period, thenormal terminals that set the normal DIFS/AIFS [AC] period (the OFDMAtarget terminals, the base station, etc.), at the next access.

Currently, conditions of setting the EIFS period include a case wherethe process of receiving PLCP (Physical Layer Convergence Procedure) isnot correctly finished and a case where an error is detected in the FCStest on the MAC frame. In the case where the process of receiving PLCPis not correctly finished, control is performed so that an error can benotified in PHY-RXEND.indication to the MAC layer, and the EIFS periodcan be set on the MAC layer. Examples where the process of receivingPLCP cannot be correctly finished and an error in PHY-RXEND.indicationis notified include a case where the MCS (Modulation and Coding Scheme)notified in the physical header is not supported (Unsupported Rate), acase of format violation, and a case of carrier lost. A case where theOFDMA non-target terminal described before perform decoding only up tothe middle of the header of the physical packet also correspond to thecase where the process of receiving PLCP cannot be correctly finished.It can be considered that an error is notified on the MAC layer inPHY-RXEND.indication.

Hereinafter, referring to FIG. 4 , occurrence of the inequality ofaccess to the wireless medium between the OFDMA target terminals and thebase station and the OFDMA non-target terminals after OFDMAcommunication is specifically described. FIG. 4 shows an operationsequence example in a case of OFDMA communication between base station(AP) 101 and terminal (STA) 1 to terminal (STA) 4. For the sake ofdescription, it is assumed that terminals 1 to 4 and non-targetterminals 5 and 6 have the capabilities of OFDMA communication and thecapabilities are enabled but do not have the function of solving theunfairness pertaining to the characteristics of this embodiment. In abottom part of FIG. 4 , an operation example of terminals 5 and 6, whichare OFDMA non-target terminals, is also shown.

In the sequence example, base station 101 and terminals 1 to 4 performOFDMA communication (both of downlink transmission and uplinktransmission) using a continuous 20 MHz width frequency band in one 20MHz width channel. The base station allocates one or more continuoussubcarriers as resource blocks to the terminals on the basis of thesubcarriers orthogonally arranged in the 20 MHz width band. In thisexample, it is assumed that four resource blocks 1, 2, 3 and 4 are setin one channel, and resource blocks 1 to 4 are sequentially allocated torespective terminals 1 to 4 in a descending order of frequency.According to description in conformity with the example shown in FIG. 2, the case correspond to the case where K=4 is assumed, the fourresource blocks set in channel M are sequentially allocated torespective terminals 1 to 4 in the descending order of frequency.

Base station 101 simultaneously transmits MAC frames to terminals 1 to 4using resource blocks 1 to 4 in the channel (downlink OFDMAtransmission). More specifically, the physical packets containing framesdestined for terminals 1 to 4 are transmitted in respective resourceblocks 1 to 4 on the basis of the access right on the medium of oneframe obtained by preliminary carrier sensing of the channel. In theexample in FIG. 4 , the frame lengths of the MAC frames contained in thephysical packets are the same.

FIG. 5A is a diagram showing a schematic format example of a physicalpacket according to this embodiment. This format contains a physicalheader and a data field. On the beginning side of the physical header,L-STF, L-LTF and L-SIG fields are arranged. After these fields, thefields of preambles 1 and 2 according to this embodiment are arranged.Preamble 1 and 2 may be newly defined fields, or extensions of thefields after L-STF, L-LTF and L-SIG in an existing standard. Forexample, in the physical packet format of IEEE 802.11ac, which is theexisting standard, VHT-SIG-A may be extended to define preamble 1, andVHT-SIG-B may be extended to define preamble 2. In at least one of aposition between preambles 1 and 2, a position before preamble 1, or aposition after preamble 2, another field may reside. For example,between preambles 1 and 2, STF and LTF fields may be arranged in thisorder. STF and LTF fields may be newly defined fields, extensions ofVHT-STF and VHT-LTF of an existing standard, or fields identical tothese fields.

L-STF, L-LTF and L-SIG are fields recognizable by the legacy terminal inconformity with IEEE 802.11a or the like (the beginning L representslegacy), and contain information on signal detection, frequencycorrection, transmission rate (or MCS) and the like. L-STF, L-LTF andL-SIG are required to be transmitted in the channel width band (20 MHz)so as to be received and decoded by legacy terminals. Consequently, in acase of OFDMA transmission to multiple terminals in multiple resourceblocks in one channel, the contents of L-STF, L-LTF and L-SIG ofphysical packets transmitted to the terminals are required to be thesame. Accordingly, even the legacy terminals can receive and decodeL-STF, L-LTF and L-SIG common to these physical packets.

L-STF, L-LTF and L-SIG are sometimes called legacy fields in acollective manner. FIG. 4 shows the legacy field as a rectangle overfour resource blocks so as to represent that the legacy field istransmitted in channel width band (20 MHz).

Preamble 1 transmitted by the base station contains information commonlyrecognizable by the OFDMA compatible terminals. Information set inpreamble 1 of the header of the physical packet to be OFDMA-transmittedfrom the base station to multiple terminals may be, for example,information that identifies multiple terminals (target terminals)serving as OFDMA transmission targets. The information for identifyingthe multiple terminals may be information (identifiers) thatindividually identifies (identify) these terminals, or the group ID of agroup to which the multiple terminals commonly belong. The group ID isallocated by the base station and notified to the terminals when orafter the terminals join the BSS of the base station (i.e., at the timeof association process). The base station can generate and managemultiple groups, and grasps the terminals on a group-by-group basis. Insome cases, an identical terminal belongs to multiple groups. When thegroup to which the terminal belongs is changed, the changed group ID isnotified to the terminal. Examples of information for identifyingindividual terminals include association IDs (AIDs) assigned by the basestation at the time of association with the base station, or theterminals' MAC addresses, and both of them. The information forindividually identifying the terminals are not limited to the examplesdescribed here as long as the terminals can be identified.

Another example of information set in this preamble 1 may be informationfor identifying the resource blocks used by the OFDMA target terminals.For example, in a case where terminals 1 to 4 are designated as targetterminals, information for identifying resource blocks 1 to 4 may be setfor terminals 1 to 4. More specifically, multiple fields that designatethe number of resource blocks may be provided, and the resource block tobe used may be identified on the basis of the number of resource blocksdesignated by the field at the position for the own terminal (sometimescalled the user position). In this case, the position of the field forthe own terminal is preliminarily notified at the time of association orany timing thereafter. The number of resource blocks allocated torespective terminals may be allocated to terminals in a descending orderof precedence of field position. At this time, the order of allocationis defined in each of the resource blocks. The resource blocks areallocated in this order. In the example described before, one is set, asthe number of resource blocks, in each of the fields for terminals 1 to4. In this case, it is preliminarily defined that allocation isperformed according to the order of resource blocks 1 to 4.

In a case where identifiers for individually identifying the respectiveresource blocks are defined, the identifiers of the resource blocks asmany as the number of resource blocks to be used may be allocated at thepositions (user positions) of the fields for the respective terminals inpreamble 1. Alternatively, the correspondence information between theidentifier, such as AID of the terminal, and the identifier of theresource block to be used by the terminal may be set in preamble 1.

Preamble 1 may contain information pertaining to the scheme (LDPC (LowDensity Parity Check), convolution, etc.) of error correction code usedfor at least one of preamble 2 or the data field.

Preamble 1 may contain the total number of resource blocks used forOFDMA. For example, in a case where the resource block used in thechannel is identified according to the total number of resource blocksused in one channel width band (e.g., the total number of resourceblocks from the side of high frequency side or the low frequency side),the resource block used in OFDMA communication can be identified on thebasis of the total number. Alternatively, in a case where thearrangement of resource blocks (the correspondence between resourceblocks and subcarriers) varies according to the total number, theresource block used in OFDMA communication can be identified on thebasis of the total number.

Preamble 1 may contain information pertaining to the intervals betweenthe resource blocks (the number of subcarriers residing between adjacentresource blocks). For example, in a case where multiple arrangementpatterns of resource blocks used for OFDMA exist in the channel and theintervals between resource blocks are different among the arrangementpatterns, the resource block used for OFDMA communication may beidentified on the basis of information pertaining to the intervals.

Each terminal may grasp the correspondence between each of the resourceblocks and the subcarriers belonging to the resource block. Thecorrespondence may be predefined by the system or specifications.Alternatively, the correspondence may be defined by the base station,and may be notified in the beacon frame, an association response frame,a newly defined frame, any control frame or the like, at the time ofassociation with the terminal or at another timing. As described before,the correspondence between the resource block and subcarriers can varyaccording to the number of resource blocks to be used, in some cases.The resource block used by the terminal may be predetermined. In thiscase, in preamble 1, setting of information for identifying the resourceblock used by the terminal may be omitted. Preamble 1 which isuplink-transmitted from the terminal to the base station stores thereininformation recognizable by the base station (information identifyingthe base station etc.).

Preamble 1 is transmitted in channel width band (20 MHz) as with thecase of the legacy field. Consequently, in a case where the physicalpacket is OFDMA-transmitted to multiple terminals in multiple resourceblocks in one channel, the content of preamble 1 of the physical packettransmitted to the terminals is required to be the same. The OFDMAcompatible terminal having received preamble 1 receives and decodes thesignal in the channel width band. FIG. 4 shows preamble 1 as a rectangleover four resource blocks so as to represent that preamble 1 istransmitted in channel width band (20 MHz). L-STF, L-LTF, L-SIG andpreamble 1 are comprehensively called a common preamble, in some cases.

Preamble 2 stores information required to decode the data field withrespect to each corresponding resource block. For example, themodulation and coding scheme (MCS: Modulation and Coding Scheme)required to decode the MAC frame in the data field transmitted in theresource block is stored. Preambles 2 are transmitted to the targetterminals in the bands for the respective resource blocks, instead ofone channel width band. That is, preambles 2 are transmitted byfrequency multiplexing. The OFDMA target terminal determines that theown terminal is designated in preamble 1, subsequently receives preamble2 in the resource block designated in preamble 1 or having preliminarilybeen designated, and preamble 2 is decoded, thereby obtaininginformation, such as MSC, required to decode the data field (MAC frame).Preambles 2 are transmitted to the terminals in the bands for therespective resource blocks, and the contents may be different from eachother. Note that if the contents of preambles 2 are the same, no problemoccurs. Preamble 2 and the data field are common in that transmission isperformed with respect to each resource block. Consequently, it can beregarded that a field containing preamble 2 and the data field exists.In this case, the field contains preamble 2 and the data field, and mayfurther contain another field as long as the other field is transmittedin the same resource block. FIG. 4 illustrates preambles 2 in rectanglesseparated among resource blocks so as to represent that preambles 2 aretransmitted in bands for the respective resource blocks. Numeralsdescribed in the rectangles representing preamble 2 indicate the numbersof terminals serving as destinations, for the sake of convenience. Forexample, rectangular preamble 2 in which numeral 1 is written means thatinformation destined for terminal 1 is contained but does not mean thatinformation for identifying the terminal is contained (it is a matter ofcourse that the information for identifying the terminal may becontained).

The data field contains the MAC frame. As with preambles 2, the MACframes are transmitted in bands for the resource blocks to therespective terminals. That is, the data fields are transmitted byfrequency multiplexing. The MAC frames transmitted in the resourceblocks are frames destined for the respective terminals. The contents ofthese MAC frames may be different from or the same as each other. TheMAC frames transmitted in the respective resource blocks may be any ofthe data frames, management frames and control frames, and a combinationthereof. The data frame may not only be the single MAC frame but also bean aggregation frame (A-MPDU) or the like in which multiple MAC framesare aggregated. In the example in FIG. 4 , the data frame is set in thedata field of the physical packet which is downlink-OFDMA-transmittedfrom the base station. The diagram illustrates this as “MPDU (Data)”. Asdescribed before, “MPDU” may indicate not only a single MAC frame butalso an aggregation frame (A-MPDU) or the like. This embodiment assumesthe aggregation frame. FIG. 4 illustrates the MAC frame in rectanglesseparated among resource blocks so as to represent that the MAC frame(data frame) is transmitted in the bands for the respective resourceblocks, in a manner analogous to that of preamble 2. Numerals describedin the respective rectangles indicate numbers of terminals serving asdestinations, for the sake of convenience. For example, the rectangularMAC frame in which numeral 1 is written is a frame destined for terminal1 (e.g., RA is the MAC address of terminal 1).

The format of each field of the physical header has been describedmainly assuming the case of downlink OFDMA communication. In a case ofanother type of communication, the format of the field (preamble 1,preamble 2, or both of these preambles) may be different according tothe type of communication.

As described before, as for the physical packet that isOFDMA-transmitted from the base station, the legacy field and preamble 1are transmitted in the channel bandwidth, and preamble 2 and the datafield are transmitted in units of resource blocks. That is, in thiscase, the physical packet that is OFDMA-transmitted from the basestation contains the legacy field and preamble 1 that are common to thetarget terminals, and multiple preambles 2 and multiple data fields on aterminal-by-terminal basis, as shown in FIG. 5B. The physical headercontains the legacy field and preamble 1 that are common to the targetterminals, and multiple preambles 2 on a terminal-by-terminal basis.

FIG. 6 is a diagram showing a basic format example of a MAC frame. Thedata frame, management frame, and control frame basically include such aframe format. This frame format includes a MAC header, a Frame bodyfield, and a FCS field. The MAC header includes a Frame control field, aDuration field, an Address 1 field, an Address 2 field, an Address 3field, a Sequence Control field, a QoS Control field and an HT (HighThroughput) control field. Not all of these fields do not necessarilyexist. Alternatively, some fields do not exist in some cases. Anotherfield that is not shown in FIG. 6 may exist. For example, an Address 4field may further exist. The Address 1 field stores therein a ReceiverAddress (RA). The Address 2 field stores therein a Transmitter Address(TA). The Address 3 field stores therein a BSSID (Basic Service SetIDentifier) which is the identifier of a BSS (in some cases, all thebits are set to 1 for all the BSSIDs as targets; wildcard BSSID) or aTA, according to the usage of the frame.

In the Frame Control field, two fields that are Type and Subtype are setas described before. Broad discrimination among the data frame,management frame and control frame is made according to the Type field.Narrow discrimination in the broadly discriminated frames, for example,identification of the BA frame, BAR frame, and a Beacon frame in themanagement frame, is made according to Subtype field.

As described before, in the Duration field, the medium reservationperiod is described. When a MAC frame destined for another terminal isreceived, it is determined that the medium is virtually busy over themedium reservation period from the end of the physical packet containingthe MAC frame. Such a scheme for determining that the medium isvirtually busy, or the duration during which the medium is virtuallyregarded to be busy is called a NAV (Network Allocation Vector) asdescribed before.

The QoS field is used for QoS control that is for transmission inconsideration of the precedence of the frame. The HT Control field is afield introduced in IEEE 802.11n, and exists in a case where the frameis a QoS data frame or a management frame and when the Order field isset to one. The an HT Control field can be extended to a VHT (Very HighThroughput) Control field of IEEE 802.11ac and also to a HE (HighEfficiency) Control field of IEEE 802.11ax, which is the next generationLAN standard. In such cases, notification can be made according tovarious functions of IEEE 802.11n, IEEE802.11ac or IEEE 802.11ax.

In the management frame, an information element (Information Element;IE) assigned the unique Element ID (IDentifier) is set in the Frame Bodyfield; and one or more information elements can be set. The informationelement is identified by the Element ID, and includes fields which arean Element ID field, a Length field, and an Information field. TheInformation field stores therein the content of information to benotified. The Length field stores therein information on the length ofthe Information field. In the FCS field, FCS (Frame Check Sequence)information is set as a checksum symbol used to detect an error in theframe on the receiver side. An example of the FCS information may be CRC(Cyclic Redundancy Code) or the like.

In the sequence of FIG. 4 , terminals 1 to 4 receive and decode thephysical packets transmitted in the multiple resource blocks from basestation 101, and obtain the MAC frames allocated to the respectiveterminals. An error test is performed on the basis of the FCS of theobtained MAC frame. If there is no error, the header and the frame bodyfield (data main body) are processed. For example, in the case of thedata frame, data stored in the frame body field is output to the upperlayer. In the case of the management frame or control frame, anoperation for management or control according to information containedin the frame body field is performed. Here, it is assumed that the MACframe is an aggregation frame that contains multiple data frames.

Terminals 1 to 4 generate acknowledgement response frames eachcontaining bitmap information indicating whether the corresponding dataframe has successfully been received or not, on the basis of the resultof error test for the corresponding data frame in the aggregation frame.Terminals 1 to 4 each transmit a physical packet that contains a BAframe (Block ACK frame) that is an acknowledgement response frame in thesame resource block as the resource block in which the MAC frame hasbeen received, SIFS-period after completion of reception of the framefrom the base station. The uplink OFDMA transmission has thus beenperformed from terminals 1 to 4 to base station 101. The lengths of BAframes transmitted from the respective terminals are assumed to be thesame as each other. The SIFS period is an example. Alternatively, anyperiod may be adopted as long as the period is a certain constantperiod. This applies to every representation of SIFS period in thefollowing description. As with the physical packet which isOFDMA-transmitted from the base station, the legacy field and preamble 1of the physical packet containing the BA frame is transmitted in thechannel width band (20 MHz width band). Preambles 2 and the MAC framesthat are fields after preamble 1 are transmitted in the bands for therespective resource blocks. To represent these features, in FIG. 4 , thelegacy field and preamble 1 in the header of the physical packettransmitted by each terminal is represented as a rectangle over fourresource blocks, and subsequent preambles 2 and the MAC frames arerepresented as rectangles contained only in the respective resourceblocks. “AP” described in the rectangle representing the MAC frame meansthat the destination of the MAC frame is the base station (e.g., RA isthe BSSID or MAC address of the base station).

Here, the physical packets which is OFDMA-transmitted in resource blocks1 to 4 from the base station are received even by terminals other thanterminals 1 to 4 only if the terminals are in states capable ofreceiving the signal from the base station. For example, the physicalpacket is received even by the non-target terminal (here, terminals 5and 6). At this time, in a typical case, it is believed that thenon-target terminal (without the function of this embodiment) decodespreamble 1 of the header of the physical packet, and resultantly decodesno field thereafter, and detects an error assuming that the physicalpacket has not been received correctly. In this case, the non-targetterminal sets the EIFS period in carrier sensing at the next channelaccess, as described before. For example, at the time of completion ofdownlink OFDMA transmission of physical packets from the base station inFIG. 4 , CCA becomes idle. In a case where the OFDMA non-target terminalperforms carrier sensing for obtaining a channel access right, the EIFSperiod is set for carrier sensing in a certain period before backoff(see “EIFS SETTING 1” in FIG. 4 ). Likewise, also in a case wheremultiple physical packets are OFDMA-transmitted from multiple targetterminals to the base station, the non-target terminals cannot receivethe MAC frames in the physical packets correctly, and a reception erroroccurs. For example, as a result of decoding the legacy field andpreamble P1, it is determined that the physical packet is not related tothe own terminal, and a reception error is detected assuming thatdecoding of fields thereafter is not to be performed. Even if preamble 2and the MAC frame of the field thereafter are received, the signal inwhich the signals from multiple terminals are duplicated is tried to bedecoded. Consequently, the signal is not correctly decoded. A receptionerror is detected anyway. As a result, in carrier sensing at the nextchannel access, the EIFS period is set as carrier sensing in a certainperiod before backoff. For example, as shown in FIG. 4 , at the time ofcompletion of uplink OFDMA transmission of physical packets frommultiple target terminals, CCA becomes idle. In a case of carriersensing for obtaining a channel access right, the EIFS period is set forcarrier sensing in a certain period before backoff (see “EIFS SETTING 2”in FIG. 4 ). The reception errors can include not only the exampledescribed here but also the examples described before, for instance, theexample where MCS is not supported (Unsupported Rate) and the examplewhere the carrier is lost (Carrier Lost).

Here, the EIFS period is described. For example, the EIFS period isdefined as a period obtained by adding an SIFS period, an ACK frame timelength (the length of a period required to transmit an ACK frame) and aDIFS/AIFS [AC] period together.

That is,

-   -   EIFS period=SIFS period+ACK frame time length+DIFS/AIFS [AC]        period.

The AIFS is an IFS determined based on the DIFS further in considerationof the concept of QoS (Quality of Service). AC of AIFS [AC] means anaccess category. The value of AIFS is set according to the priority(access category) determined according to the type and the like of datato be transmitted. The higher the priority is, the lower the value ofAIFS is (the backoff period is also set advantageously).

In a case of performing carrier sensing for obtaining the channel accessright after OFDMA communication, the OFDMA target terminal or basestation sets a normal period, i.e., the DIFS/AIFS [AC] period, as acertain period of carrier sensing to be performed before backoff, unlessthere are special circumstances, such as a reception error. Here,DIFS/AIFS [AC] period means one of DIFS and AIFS [AC] periods. The casewithout consideration of the QoS of data indicates the DIFS period. Thecase with consideration of the QoS indicates the AIFS [AC] perioddetermined according to the type and the like of data to be transmitted.According to the relational expression of the EIFS period describedbefore, the EIFS period is longer than the DIFS/AIFS [AC] period.Consequently, the terminal having detected a reception error is moredisadvantageous in obtainment of the access right on the medium thanterminals having not detected the error. FIG. 7 schematically shows thisfact. FIG. 7A schematically shows the carrier sensing period in a caseof setting the EIFS period (the sum of the EIFS period and the backoffperiod). FIG. 7B schematically shows the carrier sensing period (the sumof DIFS/AIFS [AC] period and the backoff period) in a case of settingthe DIFS/AIFS [AC] period. The EIFS period is longer than the DIFS/AIFS[AC] period. It can thus be understood that the terminal having detecteda reception error has a long standby time and is disadvantageous inobtainment of the access right. The value of the backoff periodsubsequent to the EIFS period and the DIFS/AIFS [AC] period is randomlydetermined. Even during the backoff period, the carrier sensing iscontinuously performed (backoff). The backoff is sometimes omitted.

To solve the unfairness described before, the OFDMA compatible terminalaccording to this embodiment executes the following operation as one ofthe characteristics. When the OFDMA compatible terminal according tothis embodiment receives a physical packet which isdownlink-OFDMA-transmitted from the base station and the own terminal isnot designated as the OFDMA compatible terminal by preamble 1, that is,the terminal is the non-target terminal, this terminal identifies atleast one resource block from among the resource blocks, decodes thedata field of the identified resource block, and obtains the MAC frame.To obtain the MAC frame, the data field may be decoded using theinformation (MCS information, etc.) set in preamble 2 arranged beforethe MAC frame. The non-target terminal having obtained the MAC framesets the NAV having the same period as the length of the value (thevalue pertaining to the duration of suppression of access to the medium)set after completion of MAC frame reception in the Duration field of theheader, on the basis of this value. That is, the non-target terminaldetermines that the RA of the obtained MAC frame is not the MAC addressof this terminal, i.e., not the MAC frame destined for the own terminal,thereby setting the NAV having the same length as the value set in theDuration field. The band as the target where the NAV is set is thechannel width band where the physical packet has been transmitted.According to the above operation, even receipt of the physical packetcontaining the MAC frame that is not destined for the own terminal, thenon-target terminal correctly decodes the packet. Consequently, the EIFSsetting condition described before does not hold. Setting of the NAVbased on the header of the MAC frame that is not destined for the ownterminal does not prevent the communication of the other terminals,either.

Here, it may be predetermined which resource block the non-targetterminal identifies among multiple resource blocks. For example, in acase where the resource block to be used when the own terminal isdesignated as the target of OFDMA communication is predetermined, thisresource block may be selected. Alternatively, in a case where all theresource blocks can be received or decoded, any resource block can beselected. In a case where the resource blocks used in OFDMA-transmissionby the base station are variable, preamble 1 may be decoded to grasp theresource blocks in use, and a resource block may be selected from amongthe grasped resource blocks. In a case of the non-target terminal wherethe supportable MCS is limited among MSCs usable in BSS 1, preamble 2 ofeach resource block may be decoded to identify the resource block of theMSC supportable by the own terminal, and the data field of theidentified resource block may be decoded in this MCS to obtain the MACframe.

FIG. 8 shows an operation sequence example in a case where terminals 5and 6 that are non-target terminals set the NAV on the basis of thevalue described in the Duration field of the MAC frame obtained bydecoding. The diagram is the same as FIG. 4 except in that the operationwhere terminals 5 and 6 correctly decode physical packetsdownlink-transmitted from the base station and set NAVs and theoperation of correctly decoding one of the physical packetsuplink-transmitted from terminals 1 to 4 to set (update) NAVs. It isassumed that the lengths of downlink MAC frames (data frames) (timelength) are the same as each other, and the lengths of uplink MAC frames(BA frames) are the same as each other. As for the physical packet whichis OFDMA-transmitted by base station 101, based on preamble 2 containedin one of the resource blocks, terminals 5 and 6 decode the data fieldand obtains the MAC frame. The NAV is set after the end of the MACframe, on the basis of the value of the Duration field in the header ofthe MAC frame. The values of the Duration fields are set in conformitywith the ends (coinciding with the ends of physical packets) of the MACframes which are uplink-OFDMA-transmitted by terminals 1 to 4. In theexample in FIG. 8 , the time points of the ends of theuplink-OFDMA-transmitted MAC frames are the same. Accordingly, the endsof the pieces of NAV duration are the same. Alternatively, the timepoint of the end of the NAV duration may be set at a time point after orbefore the end of the uplink MAC frame. In the case of setting the timepoint therebefore, it is preferred that the time point be a time pointafter a timing at which the non-target terminal is incapable ofrecognizing that the reception be at least reception of theuplink-transmitted physical packet (or reception of the MAC frame) andonly capable of recognizing a busy state. For example, at least a timepoint after the beginning of the legacy field is set. Terminals 5 and 6receive multiple physical packets which are uplink-transmitted fromterminals 1 to 4, and decode one of these packets in a manner analogousto the case of downlink transmission from the base station. The legacyfields and preambles 1 of these physical packets are set to valuescommon to terminals 1 to 4. The format of preamble 1 in the case ofuplink transmission may be the same as or different from the format ofdownlink preamble 1. Terminals 1 to 4 set the same value in preamble 1on the basis of a predetermined rule. The format of preamble 2 may bethe same or different from the format of downlink preamble 2. Preamble 2stores, for example, information required to decode the data field foreach resource block corresponding thereto. Terminals 5 and 6 decode thelegacy field and preamble 1, further decode preamble 2 in the resourceblock selected from among the resource blocks, further decode the datafield of the subsequent same resource block, and obtain the MAC frame.The NAV is updated on the basis of the Duration field in the header ofthe MAC frame. Terminals 5 and 6 may select the resource block to bedecoded in a manner analogous to the case of downlink transmission.Alternatively, the same resource block as the resource block selected indownlink transmission may be selected. According to the above operation,even if terminals 5 and 6 receive physical packets destined for the basestation from terminals 1 to 4, terminals 5 and 6 correctly decode one ofthese packets, thereby preventing the condition for EIFS setting frombeing satisfied. The NAV is subsequently set (up to the end of thephysical packet to be uplink-transmitted, in this case) on the basis ofthe header of the MAC frame contained in the correctly decoded packet,thereby preventing the communication of the other terminals from beinginterfered, too.

The headers of the packets which are uplink-multi-user-transmitted fromterminals 1 to 4 contain the legacy field, preamble 1 and preamble 2.However, the configuration of the header is not limited to thisconfiguration. For example, a configuration can be adopted that includesthe legacy field and preamble 1 but includes no preamble 2. In thiscase, for example, the base station may decode the data field of theuplink-multi-user-transmitted packet using decoding information (MCS,etc.) analogous to the encoding information of the downlink multi-usertransmission taken place immediately therebefore. The base stationstarts reception within a certain fixed time period, e.g., SIFS+slotperiod (total time period of SIFS and slot time), after the lastdownlink multi-user transmission. In a case where a condition that thereceived packet is an uplink-multi-user-transmitted packet is satisfied,the base station may hold the last decoding information. In a case wherethe condition is not satisfied or SIFS+slot period has elapsed, the basestation may remove the last decoding information. The decodinginformation required to decode the data field may be contained in thelegacy field or preamble 1 or both of them.

It is assumed that terminals 5 and 6 perform carrier sensing in order toobtain the access rights on the medium after the NAV duration haselapsed. During uplink OFDMA communication, one of theuplink-transmitted physical packets is selected and correctly decoded,thereby suppressing setting of the EIFS period. Consequently, as withthe normal case, the DIFS/AIFS [AC] period is set. Likewise, also in acase where base station 101 and terminals 1 to 4 start carrier sensingto obtain the access rights on the medium after uplink OFDMAtransmission, the DIFS/AIFS [AC] period is set. Consequently, theunfairness of opportunity of obtaining the access right between thetarget terminals and base station and the non-target terminals issolved. When the carrier sensing results are idle and the access rightsare obtained, terminals 5 and 6 can transmit frames (more specifically,packets with physical headers added). As an example of a packet or frameto be transmitted, what is to be described later in a fifth embodimentmay be transmitted.

In a case where the MAC frames which are downlink-transmitted from thebase station have different lengths, padding data items may be added tothe ends of short MAC frames to adjust the frames so as to have the samelength. Alternatively, in the case of consideration of differencebetween uplink MAC frames (BA frames) serving as responses, thefollowing configuration may be adopted. That is, the pieces of NAVduration are set so that the ends of the pieces of NAV duration setaccording to the respective MAC frames which aredownlink-OFDMA-transmitted from the base station can indicate the sametime point. Consequently, for example, even if the ends of uplink MACframes (BA frames) serving as responses are different, alignment of theends of the pieces of NAV duration can maintain the equality among atleast non-target terminals. Furthermore, the time point of the ends isset to coincide with the end of the longest MAC frame among the uplinkMAC frames, thereby allowing the equality to be maintained among all theterminals including the non-target terminals, target terminals and basestation.

In a case where the base station transmits multiple frames to multipleterminals (transmits multiple frames to terminals 1 to 4 in downlinkOFDMA in the example in FIG. 8 ), the transmitted multiple frames may bethe same as or different from each other. In a case where, as typicalrepresentation, it is represented that the base station transmits orreceives multiple frames or the multiple X-th frames, these frames orthe X-th frames may be the same as or different from each other. “X” maybe assigned any value according to situations.

In the operation sequence example described before, in the case wherethe OFDMA non-target terminal is implemented with a function of powersave mode, the terminal may change the operation according to whether tobe in the power save operation or not. For example, a parameter the“power save mode activated” is provided. The state is determined as astate where the power save mode operation is performed when theparameter has a value of true(1). The state is determined as a statewhere the power save mode operation is not performed when the parameterhas a value of false(0). Here, it may be configured such that thenon-target terminal identifies at least any of the resource blocks anddecodes the MAC frame to set the NAV when the parameter is false(0), andthe terminal does not perform resource block identification and MACframe decoding when the parameter is true. During the power save modeoperation, the packet receiving operation is not performed.Consequently, the EIFS setting condition does not hold. Alternatively, aparameter of power management mode may be provided. When the parameterhas a value of active(1), the mode is not the power save mode. When theparameter has a value of power save(2), the mode is the power save mode.In this case, it may be configured such that the non-target terminalidentifies at least any of the resource blocks and decodes the MAC frameto set the NAV when the parameter is active(1), and the resource blockidentification and MAC frame decoding are not performed when theparameter is power save(2). Alternatively, irrespective of power saving,the terminal may include a parameter pertaining to presence or absenceof execution of the operation according to this embodiment. When theparameter has a value of execution true(1) and the own terminal is notdesignated as an OFDMA target, at least any resource block is identifiedand the MAC frame is decoded to set the NAV. On the other hand, it maybe configured such that when the parameter has a value of executionfalse(0) and the own terminal is not designated as an OFDMA target, theresource block identification and MAC frame decoding are not performed.Thus, the power consumption can be saved. Here, it may be controlledsuch that even without resource block identification and MAC framedecoding, it is not determined to be a reception error on the physicallayer, and the EIFS period is not internally set. The value of theparameter can be set through input by a user, or switched according tothe remaining amount of battery of the terminal. For example, in a caseof a state requiring power saving, such as a case where the remainingamount of battery is equal to or lower than a threshold, the value ofthe parameter may be set to execution false(0). The value of theparameter may be switched by MAC/PHY manager 60 or MAC processor 10.

To prevent the EIFS period from being set after OFDMA communication isfinished (BA frame transmission by each target terminal is completed), aconfiguration may be considered that sequentially transmits the BAframes from each terminal in the legacy format (the format of theexisting standard without preambles 1 and 2), instead of OFDMAtransmission. In this case, the non-target terminal (and the legacyterminal) correctly receives the BA frame (NAV setting is alsoexpected), and the EIFS period can be prevented from being set. However,this configuration cannot simultaneously transmit the BA frames.Consequently, the efficiency is reduced. On the contrary, thisembodiment can prevent the EIFS period of the non-target terminal frombeing set even in the case where the BA frame is OFDMA-transmitted aswith FIG. 8 . Consequently, reduction in efficiency can also beprevented.

As described before, in this embodiment, the OFDMA non-target terminalalso decodes the data field of at least one resource block, obtains theMAC frame destined for another terminal or the base station, andanalyzes the Duration field, thereby setting the NAV. The OFDMAcompatible terminal according to this embodiment may notify whether theterminal has a capability of performing such decoding and the NAV to thebase station. The notification may be made, for example, in anassociation request frame in an association process, or throughnotification in a management frame or the like at any timing afterassociation. The base station may control execution of OFDMAcommunication on the basis of the notified capability. For example, in acase where the ratio of the number of terminals having the capabilityamong the terminals connected to the own station is equal to or lowerthan a threshold, this station may determine not to execute OFDMAcommunication or to limit the communication. Alternatively, it may bedetermined to execute OFDMA communication only in a case where the ratiois higher than a threshold. Control and determination that are differentfrom those described here may be performed.

In this embodiment, through the received physical packet, the data fieldof the resource block identified as described before is decoded toobtain the MAC frame (the MAC frame not destined for the own terminal),and the NAV is set according to the value set in the Duration field.Thus, the EIFS period can be prevented from being set, thereby allowingthe opportunities of obtaining access rights to be the same conditionsas those of the OFDMA target terminals and the base station after OFDMAcommunication.

In the sequence described before, the data field lengths (MAC framelengths) of the resource blocks OFDMA-transmitted from the base stationare the same (in the case where the terminals have different lengths ofdata items to be transmitted, the terminals adjust the lengths withrespective padding data items). As another example, as shown in FIG. 9 ,this embodiment is applicable even to a case where the data fieldlengths (PSDU lengths) of the resource blocks are different from eachother. Three examples of the method in this case are described below.

A first method adjusts and sets the NAV values (the values of Durationfields) so that the ends of the NAVs for the respective terminals can bethe same time point. In this case, if the PSDU lengths of the resourceblocks (or MPDU lengths) are different, values set in the Durationfields or the like of the respective MAC frames become differentaccordingly. Thus, the NAVs can concurrently finish, and, for example,the ends of NAVs can coincide with the end of theuplink-OFDMA-transmitted physical packet accordingly. This configurationcan also exert advantageous effects analogous to those of the sequenceof FIG. 8 . Although the OFDMA target terminals finish reception of MACframes at different timings, carrier sensing is performed in the channelwidth, and the SIFS period is measured from the time point at which thestate becomes idle, or the end of the MAC frame completely received last(more specifically, the end of the physical packet) is calculated by anymethod (e.g., the following second method) and the SIFS period ismeasured from the time point, thereby allowing the timings of uplinktransmission of the respective terminals to coincide with each other.

The second method sets information for calculating the length of aphysical packet which is downlink-OFDMA-transmitted (the length to theend of the PSDU having the largest length if PSDUs destined for multipleterminals are comprehensively regarded as one) in the L-SIG field oranother field of the physical packet. The non-target terminal calculatesthe physical packet length (occupation period) from information on thefield, and sets the NAV after the occupation period. The physical packetlength (occupation period) is the length of T2-T1 in the example in FIG.9 . The common NAV value is set in the Duration field of each MAC frame.In this case, the end of NAV is configured to coincide with the timepoint (T3 in FIG. 9 ) of the end of each BA frame (more specifically,physical packet) to be uplink-OFDMA-transmitted. The OFDMA targetterminals can cause the timings of uplink transmission to coincide in amanner analogous to the first method. Here, in an example of settinginformation for calculating the physical packet length (occupationperiod), the Rate field and Length field of the L-SIG field (defined inIEEE 802.11 standard) may be used. For example, the base stationcalculates the physical packet length (occupation period), that is, thetime length (72 Mbps) required when receiving the physical packet at anactual rate, on the basis of multiple PSDUs (MAC frames, etc.) destinedfor multiple terminals. The base station determines the values of Ratefield and Length field so that the physical packet length can becalculated on the basis of these Rate field (rate field) and Lengthfield (length field). For example, the Rate field is set to a valuerepresenting 6 Mbps. The Length field is set to the data length (whichmay be the number of octets or be in another unit) coinciding with thephysical packet length calculated as described before in the case ofreceipt of the physical packet at 6 Mbps. (The actual reception rate ishigher than 6 Mbps. It can thus be believed that the Length field has avalue shorter than an actual packet length. The actual rate isidentified by preamble 2, for example). The non-target terminalcalculates the occupation period (PPDU occupation period) of physicalpacket on the basis of the values of Rate field and Length field of theL-SIG field, and sets the NAV after the calculated occupation periodaccording to the value of Duration field (the values of NAVs in the MACframes are common as described before) read from any one of the MACframes. Every resource block can be decoded to have the same time pointat which the NAV is finished. The value set in the Rate field is notlimited to 6 Mbps. Another value may be set.

As a third method, a case is assumed where before the base stationstarts downlink OFDMA, the terminal always notifies the longest timelength (the length of T2-T1) as the finish time point of the physicalpacket (PPDU) for downlink transmission (i.e., the packet length). Inthis case, the base station sets the NAVs having the same value in theMAC frames to be downlink-transmitted. Here, it is assumed that theterminal has a configuration that does not receive the resource blockdestined for the own terminal but receives the entire PPDU. That is, theterminal does not determine the end of PSDU only for the resource blockdestined for the own terminal but performs a process of receiving theentire PPDU (i.e., all the individual resource blocks). In this case,the end of the longest PSDU is determined. Also in a case where thenon-target terminal receives the downlink-transmitted physical packet,the terminal performs the process of receiving the entire PPDU,determines the end of the PPDU (the end of the longest PSDU), and setsthe NAV on the basis of the determination. The length of NAV may beobtained from the Duration field of the MAC frame of any resource block.

In the first to third methods described before, the lengths of BA framestransmitted from the target terminals are the same as each other.However, in a case where the lengths of BA frames are different fromeach other (see FIG. 13 described later), the NAV may be appropriatelyadjusted according thereto. For example, the value of each NAV may bedetermined so that the end of each NAV can coincide with the end of theBA frame completely transmitted last, within the ranges of frameworks ofthe first to third methods. As described later with reference to FIGS.16 and 18 , after downlink OFDMA transmission, the base station maytransmit the BAR frames, and may cause the target terminals to transmitthe BA frames as the responses thereto in uplink OFDMA. In the sequencesof FIGS. 8 and 9 described before, one frame exchange (transmission andreception) of the downlink OFDMA transmission from the base station andthe uplink OFDMA transmission from the target terminals is performed.However, analogous frame exchange may be continuously performed one ormore times thereafter. Also in this case, the non-target terminal maydecode the downlink physical packet destined for another terminal anduplink physical packet destined for the base station in a manneranalogous to that described before (operation for preventing the EIFSsetting condition from being satisfied). The types of frames to beexchanged are not limited to the combination of the data frame and theBA frame.

FIG. 10 is a flowchart showing an example of the operation of the basestation according to this embodiment. The base station determinesmultiple terminals that are OFDMA targets, and the lengths of the piecesof duration pertaining to the NAVs for the respective terminals (S11).More specifically, the length of the pieces of NAV duration aredetermined so that the time points of the ends of the pieces of NAVduration can be the same, on the basis of the lengths of multiple MACframes transmitted to multiple terminals and the lengths of BA frames(more specifically, the lengths of physical packets containing BAframes) with which the terminals respond. At this time, for example, thetime point of the end of NAV duration is aligned to the end of the BAframe with which each terminal responds (the end of the BA frame that isreceived last if the ends of BA frames are different from each other).In a case where the MAC frames to be transmitted to the multipleterminals have different lengths, padding data items may be added to theends of short MAC frames to adjust the frames so as to have the samelength. The base station generates the MAC frame with the Duration fieldset to a value pertaining to the determined NAV duration length, foreach terminal (S12). The base station stores the MAC frames in therespective data fields and adds physical headers to generate physicalpackets (also S12). The physical header contains: the legacy field;preamble 1 that contains information for identifying the multipleterminals (the identifiers of the individual terminals or the group IDor both of them or the like); and preambles 2 that are for therespective terminals and contain information for decoding the datafields containing the MAC frames.

The base station transmits the legacy field and preamble 1 of thephysical packet in the band of one channel width, and subsequentlytransmits preambles 2 and data fields in OFDMA (MAC frames) (S13).

The base station receives, from the multiple terminals, the physicalpackets containing acknowledgement response frames (BA frames)containing information pertaining to the success and failure of MACframe reception through OFDMA, SIFS-period after transmission of themultiple MAC frames (S14).

FIG. 11 is a flowchart of an operation in a case where the terminal(OFDMA target terminal) according to this embodiment receives thephysical packet transmitted from the base station in OFDMA.

The terminal having received the physical packet decodes the legacyfield and preamble 1, and determines whether the own terminal isdesignated as the OFDMA target terminal (S101 and S102). Wheninformation for identifying the own terminal or the group ID to whichthe own terminal belongs is set in preamble 1, it is determined to bedesignated.

When the own terminal is not designated as an OFDMA target, the terminalidentifies at least one resource block among the multiple resourceblocks, and decodes preamble 2 and the MAC frame in the identifiedresource block (S103). On the basis of the value set in the Durationfield of the header of the MAC frame, the NAV is set after completion ofreception of the physical packet (more specifically, completion ofreception of the MAC frame in the identified resource block) (S104). Ina case of obtaining the access right on the medium after lapse of theNAV duration, a normal period (DIFS/AIFS [AC] period) is set as acertain period of carrier sensing before backoff, carrier sensing isperformed meanwhile, and subsequently carrier sensing is furtherperformed in a randomly determined backoff period. In a case where theuplink-transmitted physical packet (the physical packet containing theacknowledgement response frame) is received in the NAV duration, thephysical packet is decoded, and the NAV is updated on the basis of theDuration field of the MAC frame header contained in the physical packet.The uplink-transmitted physical packet may be multiple physical packetstransmitted from the other multiple terminals in uplink-OFDMA, or thephysical packets individually transmitted (through single usertransmission) at different timings by the other terminals.

In a case where the own terminal is designated as the OFDMA target, theterminal identifies the resource block for the own terminal, and decodesthe data field in this data block to obtain the MAC frame (S105). Theheader of the MAC frame is analyzed, and an operation according to theanalysis result is performed. In a case where the MAC frame is the dataframe (including the case of aggregation frame), for example, theacknowledgement response frame (more specifically, the physical packetcontaining the acknowledgement response) is transmitted in this resourceblock SIFS-period after completion of MAC frame reception (S106). Atthis time, also from the other terminal designated as the OFDMA target,the physical packet containing the acknowledgement response frame may besimultaneously transmitted. In this case, the multiple acknowledgementresponse frames are transmitted in uplink OFDMA.

In this embodiment, the OFDMA non-target terminal decodes the data fieldof at least one resource block among the multiple resource blocks. In acase where the data fields of two or more resource blocks can bedecoded, that is, a case where the own terminal supports the modulationand coding schemes for preambles 2 in two or more resource blocks, aresource block with a modulation and coding scheme satisfying apredetermined condition may be selected. For example, the resource blockaccording to the most robust modulation and coding scheme may beselected. The most robust modulation and coding scheme may be, forexample, the modulation and coding scheme having the lowest transmissionrate, or the modulation and coding scheme having the lowest coding rate.According to another condition, the resource block having the modulationand coding scheme equal to or lower than a certain transmission rate ora certain coding rate may be selected. Such selection can reduce thepossibility of detecting an error in the FCS of the frame. Consequently,the possibility of correct decoding becomes improved.

Even if preamble 1 is set to the group ID of the group to which the ownterminal belongs, the MAC frame obtained from the resource block for theown terminal can sometimes be not destined for the own terminal (a casewhere RA is not the address of the own terminal or the like) accordingto the result of analysis of this MAC frame. Also in this case, the NAVmay be set on the basis of the value described in the Duration field ofthe obtained MAC frame. Thus, the normal decoding operation isperformed, and the EIFS setting condition is not satisfied.

In the embodiment described above, the NAV is set on the basis of theDuration field. Alternatively, the value of the length of the periodduring which the NAV is set may be set in preamble 1, multiple preambles2 or both of these preambles in the physical header. At this time, thevalues of the lengths of pieces of NAV duration may be determined sothat the ends of the pieces of NAV duration become the same time point,for the respective MAC frames. The terminal extracts the value fromamong preamble 1 and multiple preambles 2, and sets the NAV after thetime point of the end of the data field or the MAC frame in thecorresponding resource block during the duration indicated by thisvalue.

According to this embodiment as described above, when the terminal(non-target terminal) that is not designated as an OFDMA target receivesthe physical packets OFDMA-transmitted from the base station, theterminal decodes the MAC frame (the MAC frame destined for anotherterminal) in at least one resource block among the resource blocks, andsets the NAV on the basis of the medium reservation period set in theDuration field of the header. Thus, a decoding operation analogous tothat in the case of correctly receiving the MAC frame destined foranother terminal is performed. Consequently, an error in the PLCPreceiving process in the non-target terminal and an error of testing theMAC frame (FCS error) can be prevented from occurring, and the EIFSperiod can be prevented from being set during carrier sensing to beperformed in subsequent access right acquisition.

Second Embodiment

The first embodiment has mainly described the mode of maintaining theequality of opportunity of obtaining access rights among the OFDMAnon-target terminals and the target terminals and the base station. Thisembodiment shows a mode that can maintain the equality of opportunity ofobtaining access rights not only for the OFDMA non-target terminals butalso legacy terminals.

FIG. 12 is a diagram showing a first example of an operation sequenceaccording to the second embodiment. The difference from the operationsequence of FIG. 8 in the first embodiment is mainly described. As withthe first embodiment, terminals 1 to 6 are OFDMA compatible terminals.Among these terminals, terminals 1 to 4 are assumed as OFDMA compatibleterminals, terminals 5 and 6 are assumed as OFDMA non-target terminals.Terminals 7 and 8 are assumed as legacy terminals.

As with the first embodiment, base station 101 simultaneously transmitsMAC frames destined for terminals 1 to 4 to terminals 1 to 4 usingresource blocks 1 to 4 in the channel (downlink OFDMA transmission).SIFS-period after receipt of the physical packets, terminals 1 to 4simultaneously transmit (uplink-OFDMA-transmit) the physical packetscontaining acknowledgement response frames using resource blocks 1 to 4.More specifically, the legacy field and preamble 1 are transmitted inthe channel width band, and preambles 2 and the data fields(acknowledgement response frames) are transmitted in the resourceblocks. In the operation sequence of FIG. 8 in the first embodiment,during downlink-OFDMA-transmission from the base station, terminals 5and 6 that are the OFDMA non-target terminals decode the legacy fieldand preamble 1 and decode preamble 2 and the MAC frame in at least oneselected resource block, and set the NAV on the basis of the valuedescribed in the Duration field of the header of the MAC frame.According to this sequence, such an operation is not required to beperformed. Consequently, in a case where terminals 5 and 6 try to obtainaccess rights after completion of downlink OFDMA transmission, uplinkOFDMA transmission, or completion of both of the transmissions, theseterminals set the EIFS period (see “EIFS SETTING 1” and “EIFS SETTING 2”at the bottom of FIG. 12 ). Terminals 7 and 8 that are the legacyterminals set the EIFS period in an analogous case. Alternatively,terminals 5 and 6 may operate in a manner analogous to that in the firstembodiment, and set the NAVs.

Base station 101 transmits the CF-End frame SIFS-period after completionof receipt of the BA frame uplink-OFDMA-transmitted from terminals 1 to4. The CF-End frame is a frame for announcing completion of CFP(Contention Free Period). That is, the frame is for permitting access tothe wireless medium. In this embodiment, the CF-End frame is transmittedeven in situations where CFP is not started. The RA field of the CF-Endframe is typically set to a broadcast address. “bc” in FIG. 12 meansthat the destination address of the CF-End frame is the broadcastaddress. Alternatively, the destination address of the CF-End frame maybe permitted to be a multicast address or multiple unicast addresses.The Duration field of the header of the CF-End frame is set to 0 as themedium reservation period.

The header of the physical packet containing the CF-End frame isconfigured to contain the legacy field but to contain no preamble 1 andpreamble 2. The physical packets containing the CF-End frames aretransmitted in one channel width band, and the physical packets arecorrectly received by terminals 1 to 8. Thus, the EIFS setting interminals 5 to 8 are canceled. Terminals 1 to 8 are permitted to accessthe medium after completion of reception of the CF-End frame, and setthe normal DIFS/AIFS [AC] period when intending to obtain the accessright (see “CANCELLATION OF EIFS SETTING” at the bottom of FIG. 12 ).

The CF-End frame transmission is only one example. Alternatively,another frame may be transmitted in the physical packet in the legacyformat only if the frame has a function of permitting the receivingterminal to access the wireless medium. At this time, in the frame, theDuration field or the like may set to a value pertaining to the lengthof duration during which suppression of access to the wireless medium isinstructed. The length of this duration may be set to 0, or a valuelarger than 0. Also in a case where such a frame is transmitted, eachterminal correctly receives the physical packet containing this frame.Consequently, the EIFS period is prevented from being set. The settingof the duration to 0 allows each terminal to start an operation foraccessing the medium after the finish time point of this frame isreached. In the case where the value larger than 0 is set, terminals 1to 8 can start the operations for accessing the media when the timeperiod indicated by this value has elapsed after completion of receptionof this frame.

Thus, the CF-End frames or the frames having an analogous functionprevents the EIFS periods from being set by OFDMA non-target terminals 5and 6 and legacy terminals 7 and 8. Consequently, the equality ofopportunity of obtaining the access right can be maintained among allterminals 1 to 8 and the base station. As described before, after finishof downlink OFDMA transmission or finish of uplink OFDMA transmission,or after both of them, terminals 5 to 8 may set the EIFS periods. But inany these cases, another communication continues at SIFS intervals afterthe EIFS period is set. Consequently, no access right can be obtained atall, and it can be regarded that no problem of unfairness occurs.

FIG. 13 is a diagram showing a second example of the operation sequenceaccording to the second embodiment. The difference from the operationsequence example of FIG. 12 is mainly described.

Unlike the operation sequence example of FIG. 12 , the length of MACframes (here, BA frames) uplink-OFDMA-transmitted from terminals 1 to 4are different. The lengths of MAC frames transmitted from terminals 2and 4 are shorter than those from terminals 1 and 3. The physical headerlength is assumed to be fixed. This is because even if the sizes of theMAC frames themselves are the same among the terminals, the frame timelengths (i.e., the periods required to transmit the frames) aredifferent according to the applied transmission rate or modulation andcoding scheme (MCS). According to a method of determining thetransmission rates or MCSs of the BA frames to be uplink-transmittedfrom terminals 1 to 4, the transmission rates or MSCs of the responseframes (BA frames) may be determined according to the transmission ratesor MCSs of the MAC frames transmitted from the base station to theterminals. For example, the response is made at the maximum transmissionrate among the transmission rates equal to or lower than thetransmission rate of the MAC frame received from the base station amongthe transmission rates supported by the own terminal. In such a case,according to the transmission rates or MCSs for the MAC framestransmitted from the base station to terminals 1 to 4, the transmissionrate or MCSs for frames serving as responses may sometimes be differentamong the terminals. As a result, the uplink MAC frame time lengths aredifferent among the terminals. In such a case, base station 101 comparesthe packet lengths of the physical packets received from terminals 1 to4 with each other, and transmits the CF-End frame SIFS-period aftercompletion of reception of the physical packet having the largest packetlength. In a case where the PHY header length is fixed, base station 101may compare the frame lengths of the MAC frames contained in thephysical packets received from terminals 1 to 4 with each other, andtransmit the CF-End frame SIFS-period after completion of reception ofthe longest MAC frame. Terminals 1 to 4 may set the packet lengths ofphysical packets, the MAC frame lengths, or both of the lengths in thePHY headers (legacy fields) or other fields, and base station 101 mayread the values set therein and compare the values with each other toidentify the maximum value of the physical packet, the maximum value ofthe MAC frame length, or both of the maximum values.

In the sequence example of FIG. 13 , downlink OFDMA transmission anduplink OFDMA transmission in response thereto are performed only onetime, and subsequently the CF-End frame is transmitted. Alternatively,before CF-End frame transmission, an analogous sequence may berepeatedly performed. Also in this case, the start timing at which basestation 101 starts to measure the SIFS period after receipt of theuplink-OFDMA-transmitted physical packet may be the timing of completionof reception of the physical packet having the maximum packet length asdescribed before. When the repetition of the sequence is finished, theCF-End frame may be transmitted at the timing determined in a manneranalogous to that as described before.

In the sequence example of FIG. 13 , the value of Ack policy subfield ofthe QoS control field in the header of the MAC frame in the physicalpacket OFDMA-transmitted by the base station is set to the valueindicating Normal Ack. Accordingly, terminals 1 to 4 having received thedata frames (aggregation frames) operate so as to return the BA framesSIFS-period after reception of the data frames even without receipt ofthe BA request (Block Ack Request) frames from the base station. The Ackpolicy in this case is specifically called Implicit Block Ack Request.

FIG. 14 is a diagram showing a flowchart of the operation of the basestation corresponding to the operation sequence example shown in FIG. 13. The base station determines multiple terminals that are OFDMA targets,and generates multiple MAC frames to be transmitted to the multipleterminals (S201). The base station stores these frames in the respectivedata fields and adds physical headers to generate physical packets (alsoS201). The physical header contains: the legacy field; preamble 1 thatcontains information for identifying the multiple terminals; andpreambles 2 that are for the respective terminals and containinformation for decoding the data fields containing the MAC frames.

The base station transmits the legacy field and preamble 1 of thephysical packet in the band of one channel width, and subsequentlytransmits preambles 2 and data fields (MAC frames) in OFDMA (S202).

The base station receives, from the multiple terminals, the physicalpackets containing acknowledgement response frames containinginformation pertaining to the success and failure of MAC frame receptionthrough OFDMA, SIFS-period after transmission of the multiple MAC frames(S203).

SIFS-period after completion of receipt of the physical packetcompletely received last among the physical packets, the physical packetcontaining the CF-End frame that is an example of a frame that does notrequest transmission of an acknowledgement response is transmitted(S204).

As described before, as in a case or the like where the modulation andcoding schemes (MCSs) or transmission rates are different among thedestination terminals in uplink OFDMA transmission, the acknowledgementresponse frames serving as responses or the physical packets containingthese frames sometimes have different lengths (time lengths).Consequently, in the sequence example of FIG. 13 , the base stationidentifies the physical packet having the longest packet length amongthe physical packets for the terminals, and the end of the physicalpacket is adopted as the starting point of the SIFS period before CF-Endframe transmission.

Here, according to a third example of the operation sequence of thesecond embodiment, in order to equalize the lengths of physical packetsto be transmitted by the terminals, the base station notifiesinformation on the MCSs or transmission rates applied to the responses,in the physical packets to be transmitted in OFDMA. For example, thebase station sets information for instruction on the MCS or transmissionrate to be applied to the response, in preamble 1, preambles 2, or thelegacy field. Alternatively, new fields may be defined in the physicalheaders for the respective resource blocks. The information on the MCSsor transmission rates may be set in the new fields. Alternatively, theinformation on the MCS or transmission rate applied to the response maybe set in a reserved area of any field of the header of each MAC frame,or in a field newly defined in the header of each MAC frame. It is thematter of course that the information on the MCS or transmission rateapplied to the response may be designated by a method that is other thanthat described here. In a case where the size of the acknowledgementresponse frame (the BA frame, the ACK frame or the like) is fixed,setting of the same MCS or transmission rate for each terminal allowsthe length of the response frame (the BA frame) or the physical packetcontaining this frame to be the same. Consequently, the base station isnot required to perform a process of identifying the physical packethaving the longest packet length among the received physical packets, ona terminal-by-terminal basis.

Here, the information on the MAC or transmission rate to be used inresponse to the terminals is not necessarily explicitly designated.Alternatively, the base station may transmit the MAC frames to terminals1 to 4 in downlink-OFDMA at the transmission rates that terminals 1 to 4can implicitly designate for application to BA frame transmission. Thatis, the transmission rate or MCS for the MAC frames to be transmitted indownlink-OFDMA is controlled, which allows the time length of theresponse frame (BA frame) returned from each terminal to be controlled.As described before, each terminal can determine the transmission rateor MCS for the response frame (BA frame) according to the transmissionrate or MCS for the MAC frame that has been transmitted in OFDMA fromthe base station and is destined for the own terminal. For example, theresponse is made at the maximum transmission rate among the transmissionrates equal to or lower than the transmission rate of the MAC frametransmitted from the base station and among the transmission ratessupported by the own terminal. In the case of this rule, the basestation determines the terminals' transmission rates or MCSs of the MACframes to be transmitted in downlink-OFDMA so as to equalize thetransmission rates applied to the response frames to be returned fromthe corresponding terminals.

In a specific example, the rates that the base station defines as thesupported rates and notifies to the respective terminals are assumed asrates 1 to 10. Rates 1, 2, 3, . . . , 10 becomes higher in this order.Rate 1 is the lowest and rate 10 is the highest. It is assumed thatterminal 1 supports rates 1, 4 and 7, terminal 2 supports rates 1, 4 and8, terminal 3 supports rates 1, 4 and 9, terminal 4 supports 1, 4 and 8,among rates 1 to 10. At this time, the base station identifies one ratecommonly supported by the terminals, and identifies the minimum rateamong the rates that are at least the identified rate (called the commonrate) and higher than the common rate, on a terminal-by-terminal basis.The rate that is at least the common rate and less than the minimum rateis then determined on a terminal-by-terminal basis, and the determinedrate is applied to the MAC frame to be transmitted to the correspondingterminal.

For example, rate 4 is identified as the common rate. For, terminal 1,the minimum rate among the rates higher than rate 4 is rate 7.Consequently, the base station determines the transmission rate fromamong the rates that are at least rate 4 and less than rate 7, that is,rates 4 to 6. Likewise, for terminal 2, the base station determines thetransmission rate from among rates 4 to 7. For terminal 3, the basestation determines the transmission rate from among rates 4 to 8. Forterminal 4, the base station determines the transmission rate from amongrates 4 to 7. The thus determined transmission rates are applied to theMAC frames to be transmitted to the respective terminals. Consequently,the transmission rates of the response frames of the respectiveterminals can be determined as rate 4 in a unified manner. In a casewhere downlink OFDMA transmission is to be completed by the base stationearly, the highest transmission rates among the candidate rates may bedetermined for the respective terminals.

Here, the base station may determine the sizes (the sizes of datafields) of the MAC frames to be transmitted in consideration of thetransmission rates determined for the respective terminals so as toequalize the lengths of the MAC frames to be transmitted to theterminals (assuming that the PHY header has the same header length). Ina variation example, the sizes of the MAC frames to be transmitted bythe respective terminals are made the same while the difference in MACframe length (time length) due to the difference in transmission ratemay be adjusted by transmitting padding data at the end in a case of theMAC frames having shorter lengths than the longest MAC frame has. Thus,the transmission completion timings to the respective terminals can bealigned with each other, the transmission start timing of the responseframes (BA frames) can be aligned with each other accordingly.

In some cases, the base station does not explicitly define the supportedrates. In such cases, it is assumed that each terminal selects thetransmission rate according to a rule analogous to that described aboveand responds, the transmission rate or MCS to be applied to the MACframe (aggregation frame) to be transmitted to each terminal may bedetermined from a rate set necessarily supported by the base station inconformity with the physical layer.

It has been assumed that the transmission rate or MCS to be applied tothe physical header of the physical packet is fixed. Alternatively, in acase of consideration of situations where each terminal can apply adifferent transmission rate or MCS to the physical header, theconfiguration is as follows. For example, information on thetransmission rate or MCS commonly applied to the physical header is setin preamble 1, preambles 2, the legacy field, or any multiple fieldsthereof in the PHY header of the physical packet to be transmitted bythe base station. In a case where the transmission rates or MCSs of someof the fields in the physical header are fixed, determination may bemade for the remaining fields. For example, in a case where thetransmission rates or MCSs of preambles 2 provided for the respectiveresource blocks are preliminarily, commonly defined, the transmissionrate or MCS for the common preambles (preamble 1 and the legacy field)may be designated to have the same value for each terminal.

Third Embodiment

According to the sequences shown in FIGS. 12 and 13 in the secondembodiment, the lengths of the MAC frames (more specifically, the totallengths of the lengths of preambles 2 and the lengths of the MAC frames)to be downlink-OFDMA-transmitted are the same. Consequently, theterminals' (terminals 1 to 4) transmission of the response physicalpackets SIFS-period after completion of reception of the resource blocksdestined for the respective terminals allows the transmission starttimings of the terminals to be synchronized with each other. However, ina case where the lengths of the MAC frames to bedownlink-OFDMA-transmitted, this method can cause a problem in that thetimings of the transmission deviate from each other among the terminals.The deviation in transmission timing causes a possibility that thecommon preamble (the legacy field and preamble 1) received in thechannel width band by the base station from the terminals cannot becorrectly decoded, with a certain magnitude of deviation. According tothis embodiment, even in such a case, the transmission timings of theresponse physical packets transmitted from the respective terminals canbe synchronized with each other while the equality of opportunity ofobtaining access rights can be maintained.

FIG. 15 is a diagram showing a first example of the operation sequenceaccording to the third embodiment. The difference from the operationsequence of FIG. 12 in the second embodiment is mainly described.

As with the sequence of FIG. 12 in the second embodiment, base station101 transmits the physical packets containing the MAC frames destinedfor terminals 1 to 4 using resource blocks 1 to 4 in the channel(downlink OFDMA transmission). However, the lengths (time lengths) ofMAC frames of terminals 1 to 4 are not the same. In the example of thediagram, the lengths of MAC frames transmitted by terminals 1 and 3 arethe same. Meanwhile, the MAC frame length of terminal 4 is shorter thanthese lengths, and the MAC frame length of terminal 2 is furthershorter. The Ack policy fields of the QoS control fields in the headersof the MAC frames destined for terminals 1 to 4 are set to valuesindicating Block Ack. Consequently, even when terminals 1 to 4 receivethe physical packets, the terminals operate so as not to return theacknowledgement response frames (BA frames) SIFS-period after thereception.

The base station identifies the transmission completion timing of thelongest MAC frame among the physical packets transmitted to terminals 1to 4, and transmits the BAR (Block Ack Request) frame in the channelwidth band (e.g., 20 MHz width band) SIFS-period after theidentification. The physical header of the BAR frame contains the legacyfield but contain no preambles 1 and 2. RA of the BAR frame is themulticast address of the group to which terminals 1 to 4 belong. The“mc” in the diagram means that RA of the BAR frame is the multicastaddress. It can be considered to set the broadcast address instead ofthe multicast address. The BAR frame can be correctly received even byterminals 5 and 6, which are the OFDMA non-target terminals, and byterminals 7 and 8, which are the legacy terminals. Consequently,terminals 5 to 8 correctly receive the BAR frames, thereby canceling theEIFS period setting (see “CANCELLATION OF EIFS SETTING 1” in FIG. 15 ).

Upon receipt of the physical packets containing the BAR frames which aredownlink-OFDMA-transmitted from the base station, terminals 1 to 4transmit the physical packets containing the BA frames after lapse ofthe SIFS period because RAs of the BAR frames indicate the multicastaddress of the group to which the respective terminals belong. The BARframe is a control frame, and the type and sub-type of the MAC headerare set to the respective values indicating Control and BAR. Thesequence of BA frame transmission and thereafter is analogous to that ofFIG. 12 . In a case where RA of the BAR frame is set to the broadcastaddress, a rule may be adopted where the terminal having received theMAC frame in immediately previous downlink OFDMA transmission becomesthe target of the BAR frame.

As described before, in the sequence example of FIG. 15 , the basestation transmits the physical packet containing the BAR frameSIFS-period after completion of transmission of the MAC frame having thelongest packet length (longest time length) among the physical packetswhich is downlink-OFDMA-transmitted by the base station. Thus, thetransmission timings of the BA frames transmitted by the terminals canbe synchronized with each other.

FIG. 16 shows a flowchart of the operation of the base stationcorresponding to a first example of the operation sequence according tothe third embodiment shown in FIG. 15 . The base station determinesmultiple terminals that are OFDMA targets (S301), and generates multipleMAC frames to be transmitted to the multiple terminals. The base stationstores these frames in the respective data fields and adds physicalheaders to generate physical headers (also S301). The physical headercontains: the legacy field; preamble 1 that contains information foridentifying the multiple terminals; and preambles 2 that are for therespective terminals and contain information for decoding the datafields containing the MAC frames.

The base station transmits the legacy field and preamble 1 of thephysical packet, in the band of one channel width, and subsequentlytransmits preambles 2 and data fields (MAC frames) in OFDMA (S302).

The base station generates the BAR frame for requesting transmission ofthe BA frames as the frame containing information pertaining to thesuccess and failure of reception of the MAC frame (S303), and transmitsthe physical packet containing the BAR frame SIFS-period aftertransmission completion time point of the data field transmitted lastamong the data fields (also S303).

The base station receives the physical packets containing the BA framesin OFDMA a certain period after transmission of the BAR frame, from themultiple terminals (S304). The base station transmits the physicalpacket containing the CF-End frame a certain period such as SIFS afterreception of the physical packets from the multiple terminals (S305).

In the sequence example of FIG. 15 , the lengths of the MAC frames whichare downlink-OFDMA-transmitted by the base station are not the same.However, even in a case where these frame lengths are the same as withthe sequence diagram of FIG. 12 of the second embodiment, BAR frametransmission allows the transmission timings of the BA frames to besynchronized with each other. FIG. 17 shows a sequence example in thiscase as a second example of the operation sequence according to thethird embodiment. As shown in FIG. 17 , the lengths of the data fieldsof the physical packets (the lengths of MAC frames) transmitted toterminals 1 to 4 are the same. The description of the operation in FIG.17 is self-evident according to the description of FIGS. 15 and 12 .Consequently, the description is omitted. The operation of the basestation in this case can be understood only by replacing step 304 inFIG. 16 according to the difference described before.

FIG. 18 is a diagram showing a third example of the operation sequenceaccording to the third embodiment. The difference from the operationsequence examples of FIG. 15 or 17 is mainly described.

In the sequence examples of FIGS. 15 and 17 described before, the BAframes (more specifically, the physical packets containing the BAframes) are OFDMA-transmitted from the OFDMA target terminals (terminals1 to 4) to the base station. In the sequence example of FIG. 18 ,terminals 1 to 4 return the physical packets containing the BA framesnot in OFDMA transmission but sequentially with every SIFS perioddeviation. The physical packet containing the BA frame has the legacyformat (without preambles 1 and 2, etc.). Each terminal transmits thephysical packet in the channel bandwidth (e.g., 20 MHz band).

To achieve the transmission, the base station includes information foridentifying the timing at which the OFDMA target terminals are caused toreturn the BA frames, and information for identifying the MCS (ortransmission rate) to be applied to BA frame transmission, into the BARframe to be transmitted SIFS-period after completion of downlink OFDMAtransmission. To achieve this, the BAR frame in conformity with theexisting standard may be extended. To achieve this, in the body field ofthe format of the existing BAR frame, for example, at a position afteror before BAR Information field (a field in which the sequence number orthe like of the MAC frame requested at the first time through the BARframe is set) or another position, a field for identifying BA frametransmission timing (called a transmission timing field) and a field foridentifying the MCS (or transmission rate) to be applied to the BA frame(called a transmission rate field) may be added. Alternatively, thesefields may be added in the header of the BAR frame. The non-targetterminal receives the physical packet that contains the BAR frame andhas the legacy format, thereby canceling the EIFS period settingproblem. After the reception, the non-target terminals can correctlyreceive even the physical packets containing the BA frames sequentiallytransmitted from the terminals (the physical packets containing BAframes can be correctly received because these packets have the legacyformat). Consequently, the EIFS period setting problems does not occur.Consequently, after transmission of the BA frame from the terminaltransmitting the BA frame last, the equality of opportunity of obtainingthe access rights to the wireless medium among the terminals can bemaintained in the case of obtaining the access right.

According to a method other than that of adding the transmission timingfield and the transmission rate field to the body field of the BARframe, the base station may add these fields to preamble 1 or may addthese fields to preambles 2 for the respective source blocks of thephysical packet that the base station is to transmit in downlink-OFDMA.Alternatively, these fields may be added to the headers or the bodyfields of the MAC frames carried in the physical packets to bedownlink-OFDMA-transmitted. According to a method other than the methodsdescribed here, the information for identifying the transmission timingand the information for identifying the MCS (or transmission rate) maybe notified.

As described before, the transmission timings and transmission ratesdesignated for terminals 1 to 4 are set so that the physical packetstransmitted from terminals 1 to 4 can be separated by SIFS-intervals.For example, as shown in FIG. 18 , in a case where terminals 1, 2, 3 and4 transmit, in this order, the physical packets containing the BAframes, a timing SIFS-period after completion of BAR frame transmissionis designated for terminal 1. For terminal 2, a timing is designatedthat is a timing after a total period after completion of BAR frametransmission; the total period is obtained by totalizing the SIFSperiod, BA frame time length of terminal 1 (more correctly, the timelength of the physical packet containing the BA frame), and the SIFSperiod (i.e., 2×SIFS period+BA frame time length of terminal 1).Likewise, for terminal 3, a timing is designated that is after 3×SIFSperiod+BA frame time length of terminal 1+BA frame time length ofterminal 2. Likewise, for terminal 4, a timing is designated that isafter 4×SIFS period+BA frame time length of terminal 1+BA frame timelength of terminal 2+BA frame time length of terminal 3.

To calculate the BA frame time lengths of terminals 1 to 3, thetransmission rates that terminals 1 to 3 applies to BA frametransmission are required to be determined (the BA frames assumed tohave the same size). Thus, the base station determines the transmissionrates to be applied to terminals 1 to 3, and calculates the BA frametime lengths on the basis of the respective transmission rates. Forterminals 1 to 3, the determined transmission rates are respectivelydesignated according to the method described above. There is no terminalthat transmits the BA frame after terminal 4. Consequently, thetransmission rate is not necessarily designated for terminal 4. However,the case of designating the transmission rate even for terminal 4 isherein assumed.

Upon receipt of the physical packets containing the BAR framestransmitted from the base station, terminals 1 to 4 extract informationfor identifying the transmission rate and transmission timing to beapplied to BAR frame transmission. According to the extractedtransmission rate, the BA frames are generated, and the physical packetscontaining the BA frames are generated. According to the extractedtransmission timings, the physical packets are transmitted. The physicalpackets transmitted from terminals 1 to 4 are separately transmittedwith deviation of every SIFS period, and are sequentially received bythe base station.

It has been assumed that the transmission rate or MCS to be applied tothe physical header of the physical packet is fixed. Alternatively, in acase of consideration of situations where the terminal can applydifferent transmission rate or MCS, the configuration is as follows. Forexample, each terminal set information on the transmission rate or MCScommonly applied to the physical header, in preamble 1, preambles 2, thelegacy field, or any multiple fields thereof in the PHY header of thephysical packet to be transmitted by the base station. In a case wherethe transmission rates or MCSs of some of the fields in the physicalheader are fixed, determination may be made for the remaining fields inan analogous manner. For example, in a case where the transmission ratesor MCSs of preambles 2 provided for the respective resource blocks arepreliminarily, commonly defined, the transmission rate or MCS for thecommon preambles (preamble 1 and the legacy field) may be designated tohave the same value for each terminal.

In the examples of the above description, the base station explicitlynotifies the transmission rates to be applied to terminals 1 to 4, tothese terminals 1 to 4. Alternatively, the base station may transmit theBAR frames at transmission rates that terminals 1 to 4 can implicitlydesignate for application to BA frame transmission. As described in thesecond embodiment, each terminal can determine the transmission rate orMCS for the response frame (BA frame) according to the transmission rateor MCS for the MAC frame that has been transmitted from the base stationin OFDMA and is destined for the own terminal. For example, the responseis made at the maximum transmission rate among the transmission ratesequal to or lower than the transmission rate of the MAC frametransmitted from the base station in the set of rates supported by theown terminal. The base station can thus identify the transmission ratesthat the terminals apply to responses on the basis of the transmissionrates applied to the MAC frames to be transmitted to the respectiveterminals.

In some cases, the base station does not define the supported rates. Inthis case, it may be assumed that the terminals select the transmissionrates from the rate set necessarily supported by the base station inconformity with the physical layer according to a rule analogous to thatdescribed before and respond.

The order of causing the terminals to respond with the BA frames isterminals 1, 2, 3, and 4 in the example in FIG. 18 . However, the orderof causing the terminals to respond is not limited to this order. Thebase station may determine the response order of the terminals accordingto a predetermined rule, or in any manner. For example, the responseorder of the terminals may be determined according to a rule where theterminals respond in the ascending or descending order of thefrequencies of allocated resource blocks or an order based on anothercriterion. In the case of response in descending order of frequencies,as with the example in FIG. 18 , the order is terminals 1, 2, 3 and 4.In the case of response in ascending order of frequencies, the order isterminals 4, 3, 2 and 1. The order of response of the terminals may bedetermined to be the descending or ascending order of the association ID(AID) or MAC address, or an order based on another criterion.Alternatively, in a case where a terminal having a power save moderesides, the terminal may be caused to respond with priority.

FIG. 19 is a diagram showing a flowchart of an operation of the basestation corresponding to the third example of the operation sequenceaccording to the third embodiment shown in FIG. 18 . The base stationdetermines multiple terminals that are OFDMA targets, and determines thetransmission timings of the physical packets containing the BA framesthat are response frames to the BAR frames transmitted from the basestation on a terminal-by-terminal basis (S401). The transmission timingsare determined so that the physical packets containing the BA frameswon't be received at overlapping timings. For example, the transmissiontimings are determined so that the reception intervals of the physicalpackets can be separated by every SIFS period. The base stationgenerates multiple MAC frames to be transmitted to multiple terminals.The base station stores these frames in the respective data fields andadds physical headers to generate physical packets (the same S402). Thephysical header contains: the legacy field; preamble 1 that containsinformation for identifying the multiple terminals; and preambles 2 thatare for the respective terminals and contain information for decodingthe data fields containing the MAC frames. At least one of preamble 1,preambles 2, or the MAC frames contains information for designating thetransmission timing determined on terminal-by-terminal basis.

The base station transmits the legacy field and preamble 1 of thephysical packet in the band of one channel width, and subsequentlyOFDMA-transmits preambles 2 and data fields (MAC frames) (S403).

The base station generates the BAR frame for requesting transmission ofthe BA frame (S404), and transmits the physical packet containing theBAR frame SIFS-period after transmission completion of the data fieldtransmitted last among the data fields (the same S404).

After BAR frame transmission, the base station sequentially receives,from multiple terminals, the physical packets that contain the BA framesand have been transmitted at the respective designated transmissiontimings (S405).

In the flow described above, the base station may determine themodulation and coding schemes or transmission rates that multipleterminals apply to BA frame transmission so that the receptions of theBAR frames received from the respective terminals won't overlap. In thiscase, at least one of preamble 1, preambles 2, or the MAC framescontains information for identifying the determined modulation andcoding scheme or transmission rate. Or the multiple terminals may adoptthe rule of determining the modulation and coding scheme or transmissionrate applied to the BA frames according to the modulation and codingscheme or transmission rate applied to the BAR frames. In a case wherethis rule is recognized, the modulation and coding scheme ortransmission rate applied to the BAR frames may be determined by thebase station so that the receptions of the BAR frames received from therespective terminals won't overlap.

Fourth Embodiment

The first to third embodiments have described the schemes that keep theequality of the opportunities of obtaining access rights on the mediumamong the terminals (i.e., among the OFDMA target terminals, the OFDMAnon-target terminals, and the base station) in the case of OFDMAtransmission from the base station to the multiple terminals. Likewise,also in a case of multi-user MIMO (Multi-User Multiple Input, MultipleOutput: MU-MIMO) transmission from the base station to multipleterminals, unfairness occurs in the opportunities of obtaining theaccess rights on the medium. MU-MIMO transmission from the base stationto the multiple terminals is specifically called downlink MU-MIMO insome cases. MU-MIMO transmission from the multiple terminals to the basestation is called uplink MU-MIMO in some cases. In this embodiment, aterminal that can perform at least the downlink MU-MIMO communicationbetween these downlink MU-MIMO and uplink MU-MIMO is called a MU-MIMOcompatible terminal.

In the downlink MU-MIMO transmission, a technique called beamforming isused to form among multiple terminals radio waves (beams) havingdirectionalities making the interference with each other minimum orsmall. The terminals and the formed beams are used to transmit datastreams to the respective terminals. Simultaneous transmission, that is,spatially multiplexed transmission, can thus be made from the basestation to the multiple terminals, in the same frequency band. Thefourth embodiment assumes a case where the channel width band (e.g., 20MHz width band) is used as the frequency band for MU-MIMO communication.

The schemes of preventing the unfairness in obtaining the access rightsdescribed in the first to third embodiments are also applicable to thecase of MU-MIMO transmission from the base station to the multipleterminals. Consequently, the opportunities of obtaining access rightscan be made equal between the terminals and the base station that aredesignated as the targets of MU-MIMO transmission this time (MU-MIMOtarget terminals), and the terminals that are not designated as thetargets of MU-MIMO transmission this time (MU-MIMO-non-targetterminals), among the MU-MIMO compatible terminals. The opportunities ofobtaining access rights are made equal further including legacyterminals.

The fourth embodiment is hereinafter described in detail. The differencefrom the first to third embodiments is mainly described. Variousderivatives, such as modification, enhancement, replacement, additionand exception, described in the first to third embodiments are alsoapplicable to this embodiment. Modification, enhancement, replacement,addition, exception and the like that are self-evident from thedescription of the first to third embodiments are not described againhere. A block diagram of a wireless communication device mounted on eachof the base station and terminals according to this embodiment is thesame as that of FIG. 1 . The difference of each block is only changeaccording to change of the communication scheme from OFDMA to MU-MIMO.Basically, the description of the block diagram is also applicable byreplacing OFDMA with MU-MIMO and resource blocks with the streams.

Referring to FIG. 20 , possible access unfairness is described that canoccur between the MU-MIMO-non-target terminals, and the MU-MIMO-targetterminal and the base station. FIG. 20 shows an operation sequenceexample in a case of MU-MIMO communication between base station (AP) 101and MU-MIMO target terminals (STA) 1 to 4. For the sake of description,it is assumed that terminals 1 to 4 and terminals 5 and 6 have thecapabilities of MU-MIMO communication and the capabilities are enabledbut do not have the function of solving the unfairness pertaining to thecharacteristics of this embodiment. In a bottom part of FIG. 20 , anoperation example of terminals 5 and 6, which are MU-MIMO-non-targetterminals, is also shown. The abscissa axis indicates the time, and theordinate axis indicates the space.

In the sequence example, base station 101 and terminals 1 to 4 performMU-MIMO communication (both of downlink transmission and uplinktransmission) using one channel of 20 MHz width band. Base station 101may preliminarily transmit packets for measurement or any packets fromantennas to individual terminals, and receive packets that containpieces of channel information estimated by the respective terminals.Downlink channel information between the multiple antennas of basestation 101 and one or more antennas of each terminal may thus beobtained. The channel information may be obtained by a method other thanthat described here. Base station 101 generates physical packetscontaining MAC frames destined for the respective terminals, generatesone or more streams for the respective terminals, on the basis of thegenerated physical packets, using the pieces of downlink channelinformation for the respective terminals, and transmits the streams toterminals 1 to 4.

According to the format example of the physical packet of thisembodiment, as with the first to third embodiments, on the beginningside of the physical header, legacy fields (L-STF, L-LTF and L-SIG) arearranged. After these fields, the fields of preambles 1 and 2 accordingto this embodiment are arranged. Data fields are arranged after thephysical headers. Preambles 1 and 2 adopt the same names as those in thefirst to third embodiments. However, the contents set therein aredifferent information according to the difference in scheme betweenOFDMA and MU-MIMO. OFDMA communication allocates the resource blocks tothe terminals. Meanwhile, for MU-MIMO, the resource blocks correspond tothe streams. Different information is set according to the difference.

Preamble 1 of the physical packets transmitted in MU-MIMO by the basestation stores therein information commonly recognizable by the MU-MIMOcompatible terminals. An example of the information set in this preamble1 is information for identifying multiple terminals that are the MU-MIMOtransmission targets (target terminals). The information for identifyingthe multiple terminals may be information that individually identifiesthese terminals. Alternatively, the group ID of a group to which themultiple terminals commonly belong may be set.

Another example of information set in this preamble 1 may be informationfor identifying the streams to be received by the MU-MIMO targetterminals. For example, in a case where terminals 1 to 4 are designatedas target terminals, information for designating the number of streamsmay be set for terminals 1 to 4. For example, multiple fields thatdesignate the number of streams may be provided, and the stream for theown terminal may be identified on the basis of the number of streamsdesignated by the field at the position for the own terminal (sometimescalled the user position). In this case, the position of the field forthe own terminal is preliminarily notified at the time of association orany timing thereafter. In the example described above, one is set, asthe number of streams, in each of fields for terminals 1 to 4. Inpreamble 1, information on the total number of streams used for MU-MIMOtransmission may be set. This method can be adopted in a case where thestreams used by each terminal or the number of these streams can beidentified from the total number of streams.

The stream may be decoded using the downlink channel information.Information on the downlink channel with the base station, havingpreliminarily been obtained before MU-MIMO communication, may be used.The channel information may be obtained using the physical header (e.g.,in a case with LTF for estimation, its field is used) of the physicalpacket received this time. In the latter case, if multiple streams aretransmitted to the terminal, for example, the base station may provideone or more symbols in LTF for estimation with symbols having patterns(e.g., bit sequences of 1 and 0) orthogonal to each other with respectto the streams, on a stream-by-stream basis. At this time, the patternsthat conform to the field position and are as many as the streams areallocated to the terminal by the base station. The terminal may extractthe signals of LTF parts of multiple streams coinciding with the patternof the own terminal, through calculation of the received signal and thepattern, and estimate the channel information for each stream. Thechannel information for each stream of the own terminal may be used toseparate (extract) a subsequent field concerned. Preamble 1 transmittedfrom each terminal to the base station in MU-MIMO stores thereininformation recognizable by the base station.

The legacy field and preamble 1 are transmitted in the channel widthband (non-MIMO). FIG. 20 illustrates the legacy field and preamble 1 inrespective single rectangle blocks in order to represent that the legacyfield and preamble 1 are non-MIMO-transmitted (i.e., throughomni-transmission without directionality in any specific direction).L-STF, L-LTF, L-SIG and preamble 1 are comprehensively called a commonpreamble, in some cases.

Preambles 2 store therein information (MCSs, etc.) required to decodethe MAC frames for the respective streams. Preambles 2 are transmittedby spatial multiplexing (MU-MIMO transmission). The MU-MIMO targetterminals receive preambles 2 (and subsequent MAC frames) contained inthe streams for the own terminals and decode preambles 2 to obtain theinformation on MCSs and the like, and decode the data fields on thebasis of the MCSs and the like to obtain the MAC frames. FIG. 20illustrates preamble 2 in rectangles separated in the spatial directionon a stream-by-stream basis so as to represent that preambles 2 aretransmitted in MU-MIMO. Numerals described in the rectanglesrepresenting preambles 2 indicate the numbers of terminals serving asdestinations, for the sake of convenience.

The data field contains the MAC frame. The MAC frames are transmitted byspatial multiplexing (MU-MIMO transmission). The MAC frame is the dataframe, management frame, or control frame. The data frame may not onlybe the single data frame but also be an aggregation frame (A-MPDU) inwhich multiple data frames are aggregated. FIG. 20 illustrates the MACframes in rectangles separated in the spatial direction in astream-by-stream basis so as to represent that the MAC frames aretransmitted in MU-MIMO.

Each of terminals 1 to 4 receives and decodes the legacy field, preamble1, preamble 2 for the own terminal, and the data field in the physicalpacket transmitted from base station 101, and further decodes the streamfor the own terminal to obtain the MAC frame. Unlike downlink OFDMAtransmission described in the first to third embodiments, downlinkMU-MIMO transmission performs transmission in beamforming to eachterminal, and it is basically believed that each terminal does notreceive streams (preambles 2 and data fields) other than the stream forthe own terminal.

Terminals 1 to 4 generate acknowledgement response frames eachcontaining bitmap information indicating whether the corresponding dataframes have been successfully received or not, on the basis of theresult of error test for the corresponding data frame in the aggregationframe. Terminals 1 to 4 each transmit a physical packet that contains aBA frame (Block ACK frame) that is an acknowledgement response frame inthe channel width band, SIFS-period after completion of reception of thephysical packets (completion of MAC frame reception) from the basestation. In the case of transmission in two or more streams, terminals 1to 4 may correctly transmit (omni-transmit) the legacy field andpreamble 1 of the physical packet header containing the BA frame, andform directional beams on the basis of the preliminarily obtained uplinkchannel information for the base station (information on the uplinkchannel between the multiple antennas of the terminal and the multipleantennas of the base station) and transmit preambles 2 and MAC framesthat are subsequent to preamble 1 in stream.

Here, the physical packets transmitted in beam from the base station toterminals 1 to 4 in downlink MU-MIMO may be received by terminals otherthan terminals 1 to 4. For example, the MU-MIMO-non-target terminals(here, terminals 5 and 6) may receive the beam destined for terminal 1according to the positional relationship with the base station.According to examples of the positional relationship, the terminalconcerned resides between the base station and terminal 1, or residesnear to terminal 1. At this time, according to the related art, theMU-MIMO-non-target terminal decodes preamble 1 of the header of thephysical packet, resultantly determines that the own terminal is notdesignated, does not perform decoding thereafter, and detects areception error. In this case, the non-target terminal sets the EIFSperiod in carrier sensing at the next channel access, as describedbefore (see “EIFS SETTING 1” in FIG. 20 ). Also in a case of receipt ofthe physical packets transmitted in MU-MIMO from the multiple targetterminals to the base station, a reception error is detected in ananalogous manner, and the EIFS period is set in carrier sensing at thenext channel access (see “EIFS SETTING 2” in FIG. 20 ).

The terminals that do not detect the reception error (the targetterminals, base station, etc.) set the DIFS/AIFS [AC] period in thenormal manner, thereby causing unfairness with the non-target terminals.

Thus, to solve the unfairness described before, the MU-MIMO compatibleterminal according to this embodiment performs execution of thefollowing operation. In a case of receiving the physical packettransmitted in MU-MIMO from the base station, the MU-MIMO compatibleterminal decodes the data field of the stream received by the ownterminal and obtains the MAC frame when the own terminal is notdesignated as the MU-MIMO target (in the case of the non-targetterminal). To decode the MAC frame, information on MCS and the like setin preamble 2 before the MAC frame is used. Here, in the downlinkMU-MIMO transmission, beam-transmission is made to the MU-MIMO targetterminals (terminals 1 to 4). Consequently, it is considered that thecase where the non-compatible terminal can receive preamble 2 andthereafter of the physical packet is a case where the terminal concernedresides between the base station and terminals 1 to 4 or resides near toterminals 1 to 4. Also in this case, in a reception environment with theSINR of the received signal being at least a threshold, the signal canbe decoded.

The terminal having decoded the data field to obtain the MAC frame setsthe NAV after the completion of reception of the MAC frame on the basisof the value set in the Duration field of the header thereof. It isdetermined that RA of the MAC frame is not the MAC address of the ownterminal, thereby setting the NAV. FIG. 21 shows an operation sequenceexample in a case where the non-target terminal (terminal 5 or 6 or bothof them) sets the NAV, as a first example of the operation sequenceaccording to the fourth embodiment. The operation is the same as that inFIG. 20 except the operation of the non-target terminal's setting theNAV. The non-target terminal receives the physical packet transmitted bybase station 101, and sets the NAV after the end of the MAC frame, onthe basis of the value of the Duration field in the header of the MACframe in the stream. The NAV duration is set by completion of uplinkMU-MIMO transmission, for example. Terminals 5 and 6 receive multiplephysical packets uplink-MU-MIMO-transmitted from terminals 1 to 4, anddecode one of these packets. The legacy fields and preambles 1 of thesephysical packets are set to common values. In a part of preambles 2 ofthe physical packets (or a part of preamble 1 is also allowed), thepattern signals of terminals 1 to 4 that are orthogonal to each otherare set. Terminals 5 and 6 decode the legacy field and preamble 1, andseparate corresponding preamble 2 on the basis of the preliminarilygrasped pattern signal to obtain the channel information. Terminals 5and 6 preliminarily grasp the pattern signal used by at least one ofterminals 1 to 4 and use the pattern signal. For example, the basestation may determine the pattern signals to be used for terminals 1 to6, and store therein the list that contains these signals for a case ofnotifying the list. Terminals 5 and 6 decode the remaining part ofpreamble 2 and the subsequent data field using the obtained channelinformation, and obtains the MAC frame. The NAV is updated on the basisof the Duration field in the header of the decoded MAC frame. Accordingto the above operation, even if terminals 5 and 6 receive physicalpackets destined for the base station from terminals 1 to 4, terminals 5and 6 correctly decode one of these packets, thereby preventing thecondition for EIFS setting from being satisfied. The NAV is subsequentlyset (up to the end of the physical packet to be uplink-transmitted, inthis case) on the basis of the header of the MAC frame contained in thecorrectly decoded packet, thereby preventing the communication of theother terminals from being interfered. In a case where non-targetterminals 5 and 6 perform carrier sensing to obtain the access rights onthe medium after lapse of the NAV duration, the DIFS/AIFS [AC] period iscorrectly set. In a case where base station 101 and terminals 1 to 4also try to obtain the access rights in an analogous manner, theDIFS/AIFS [AC] period is set. Consequently, the unfairness of obtainingthe opportunity of the access right between the MU-MIMO-non-targetterminals and target terminals and base station is solved.

The headers of the packets transmitted from terminals 1 to 4 inuplink-multi-user contain the legacy field, preamble 1 and preambles 2.However, the configuration of the header is not limited to thisconfiguration. For example, a configuration can be adopted that includesthe legacy field and preamble 1 but includes no preamble 2. In thiscase, for example, the base station may decode the data field of thepacket transmitted in uplink-multi-user using decoding information (MCS,etc.) analogous to the encoding information of the downlink multi-usertransmission taken place immediately therebefore. The base stationstarts reception within a certain fixed time period, e.g., SIFS+slotperiod (total time period of SIFS and slot time), after the lastdownlink multi-user transmission. In a case where a condition that thereceived packet is transmitted in uplink-multi-user is satisfied, thebase station may hold the last decoding information. In a case where thecondition is not satisfied or SIFS+slot period has elapsed, the basestation may remove the last decoding information. The decodinginformation required to decode the data field may be contained in thelegacy field or preamble 1 or both of them. In a case where the headercontains no preamble 2, the data fields received from terminals 1 to 4may be separated by preliminarily obtaining channel information throughsounding for each of terminals 1 to 4 or through another method and thenusing this channel information.

Terminals 1 to 4 may transmit the BA frames through normal transmission(omni-transmission) sequentially in a legacy format (not containingpreambles 1 and 2), instead of uplink MU-MIMO transmission.Consequently, the non-target terminal (and legacy terminal) cancorrectly receive and decode the uplink-transmitted physical packet, andset the NAV, thereby preventing the EIFS period from being set. However,in comparison with the case where the BA frames are transmitted inuplink-MU-MIMO, a longer time is required to receive all the BA frames,and the efficiency is decreased. As described in the above embodiments,to cause the terminals to sequentially transmit the BA frames, it ispreferred to perform control so that the physical packets containing theBA frames can be separately transmitted from the terminals withdeviation of every SIFS period.

FIG. 22 is a diagram showing a second example of the operation sequenceaccording to the fourth embodiment. This operation sequence examplecorresponds to the operation sequence example in FIG. 12 according tothe second embodiment. It is assumed that terminals 1 to 6 are MU-MIMOcompatible terminals, terminals 1 to 4 thereamong are MU-MIMO targetterminals, and terminals 5 and 6 are MU-MIMO-non-target terminals.Terminals 7 and 8 are assumed as legacy terminals.

Base station 101 transmits the physical packets containing the MACframes destined for terminals 1 to 4 by spatial multiplexing (downlinkMU-MIMO transmission). Terminals 1 to 4 transmit the physical packetscontaining the acknowledgement response frames by spatial multiplexing(uplink MU-MIMO transmission) SIFS-period after completion of receptionof the MAC frames. Terminals 5 to 8 can receive any of the physicalpackets transmitted to terminals 1 to 4, or the physical packetstransmitted from terminals 1 to 4 to the base station, according to thepositions at which the respective terminals reside. In a case of receiptof any physical packet, for example, terminals 5 and 6 determine thatpreamble 1 does not contain information for identifying the ownterminal, and thus detect a reception error. Terminals 7 and 8 detect areception error because of a format error, such as incapability ofanalyzing preamble 1. In a case of trying to obtain access rights aftercompletion of downlink MU-MIMO transmission, uplink MU-MIMOtransmission, or completion of both of the transmissions, the EIFSperiod is set (see “EIFS SETTING 1” and “EIFS SETTING 2” at the bottomof FIG. 22 ).

Base station 101 transmits (omni-transmits) the CF-End frame SIFS-periodafter completion of receipt of the BA frame transmitted inuplink-MU-MIMO from terminals 1 to 4. The physical packets containingthe CF-End frames are correctly received by terminals 1 to 8.Consequently, terminals 1 to 8 are permitted to access the medium aftercompletion of reception of the CF-End frame, and set the normalDIFS/AIFS [AC] period when intending to obtain the access right (see“CANCELLATION OF EIFS SETTING” at the bottom of FIG. 22 ).

Thus, the CF-End frame prevents the EIFS period in terminals 5 to 8 frombeing set. Consequently, the equality of opportunity of obtaining theaccess right can be maintained among all terminals 1 to 8 and the basestation. As described before, instead of the CF-End frame, another framethat does not request transmission of an acknowledgement response may betransmitted. This analogously applies to the following description.

FIG. 23 shows a third example of the operation sequence according to thefourth embodiment. This operation sequence example corresponds to theoperation sequence example in FIG. 13 according to the secondembodiment.

This example is different in the lengths of MAC frames (here, BA frames)transmitted in uplink-MU-MIMO from terminals 1 to 4. The lengths of MACframes transmitted from terminals 2 and 4 are shorter than those fromterminals 1 and 3. Base station 101 transmits the CF-End frameSIFS-period after completion of reception of the physical packet havingthe largest packet length among the physical packets received fromterminals 1 to 4. In a case where the PHY header length is fixed, theCF-End frame may be transmitted SIFS-period after completion ofreception of the MAC frame having the largest frame length among the MACframes.

According to a fourth example of the operation sequence according to thefourth embodiment, in order to equalize the lengths of physical packetstransmitted by the terminals, the base station may notify information onthe MCS or transmission rate applied to response, in the physical packetto be transmitted in downlink-MU-MIMO by the base station. Consequently,the base station is not required to identify the physical packet havingthe longest physical packet among the physical packets on aterminal-by-terminal basis. The information on MAC or transmission rateused to response is not necessarily explicitly designated as describedin the previous embodiments. Alternatively, terminals 1 to 4 maytransmit the MAC frames to terminals 1 to 4 in downlink-MU-MIMO at thetransmission rates that terminals 1 to 4 can implicitly designate forapplication to BA frame transmission.

FIG. 24 shows a fifth example of the operation sequence according to thefourth embodiment. This operation sequence example corresponds to theoperation sequence example in FIG. 15 according to the third embodiment.

Base station 101 transmits the physical packets containing the MACframes destined for terminals 1 to 4 by spatial multiplexing (downlinkMU-MIMO transmission). However, the lengths of MAC frames to betransmitted to terminals 1 to 4 are not the same. The base stationtransmits (omni-transmits) the BAR (Block Ack Request) frame SIFS-periodafter the time point of the length of the packet having the largestpacket length among the physical packets transmitted to terminals 1 to4. The BAR frame has the legacy format. RA of the BAR frame is themulticast address of the group to which terminals 1 to 4 belong. It canbe considered to set the broadcast address instead of the multicastaddress. The BAR frames are not only correctly received by terminals 1to 4 but also correctly received by terminals 5 to 8. Consequently,terminals 5 to 8 correctly receive the physical packets containing theBAR frames, thereby canceling the EIFS period setting (see “CANCELLATIONOF EIFS SETTING 1” in FIG. 15 ).

Upon receipt of the BAR frames transmitted from the base station,terminals 1 to 4 transmit the physical packets containing the BA framesby spatial multiplexing (uplink MU-MIMO transmission) after lapse ofSIFS period. If terminals 5 to 8 fail to receive the physical packets,the EIFS period setting occurs again here (“EIFS SETTING 2” in FIG. 24). However, subsequently, the CF-End frames are transmitted from thebase station, and terminals 5 to 8 correctly receive these frames,thereby canceling the EIFS period setting. That is, subsequently, whenthe non-target terminals, the target terminals and the base station tryto access the wireless medium, the DIFS/AIFS [AC] period is correctlyset.

In the sequence example of FIG. 24 , the packet lengths of the physicalpackets downlink-MU-MIMO-transmitted by the base station are not thesame among the terminals. However, also in a case where these packetlengths are the same, BAR frame transmission allows the transmissiontimings of the BA frames to be synchronized with each other in ananalogous manner. FIG. 25 shows a sequence example in this case as asixth example of the operation sequence according to the fourthembodiment. This sequence example corresponds to the operation sequenceexample in FIG. 17 according to the third embodiment.

FIG. 26 shows a seventh example of the operation sequence according tothe fourth embodiment. This operation sequence example corresponds tothe operation sequence example in FIG. 18 according to the thirdembodiment.

In this sequence example, terminals 1 to 4 do not transmit the BA framesin uplink-MU-MIMO in response to the BAR frames received from the basestation. Instead, the terminals sequentially transmit (omni-transmit)the physical packets containing the respective BA frames to the basestation with every SIFS period deviation. The physical packet containingthe BA frame has the legacy format (without preambles 1 and 2).

The base station transmits (omni-transmits) the BAR frame SIFS-periodafter completion of downlink MU-MIMO transmission. The BAR framecontains information for identifying the timing at which the MU-MIMOtarget terminals are caused to return the BA frames, and information foridentifying the MCS (or transmission rate) to be applied to BA frametransmission. The details are as described in the previous embodiments.Terminals 5 to 8 correctly receive the physical packets containing theBAR frames (set the NAVs according to the value of Duration field),thereby canceling the EIFS period setting problem. Subsequently, thephysical packets containing the BA frames sequentially transmitted fromthe respective terminals can also be correctly received. Accordingly,any event that is a cause of setting the EIFS period does not occur.Consequently, in a case where each terminal and the base station try toaccess the wireless medium after terminal 4 that is to transmit the BAframe last transmits this BA frame, each DIFS/AIFS [AC] period iscorrectly set and the equality among the terminals is maintained.

The transmission timings and transmission rates designated for terminals1 to 4 may be set so that the physical packets respectively transmittedtherefrom can be separated by SIFS-intervals, in an analogous manner tothe embodiments described above. The base station may not necessarilyexplicitly notify the transmission rates to be applied to respectiveterminals 1 to 4, to these terminals 1 to 4. In this case, the basestation may transmit the BAR frames at transmission rates that terminals1 to 4 can implicitly designate for application to BA frametransmission. The details have been described in the previousembodiments. The order of causing the terminals to respond with the BAframes is terminals 1, 2, 3, and 4 in the example in FIG. 18 . However,the order of causing the terminals to respond is not limited to thisorder.

This embodiment describes the mode of equalizing the opportunities ofobtaining access rights on the medium in the case where the base stationperforms downlink multi-user MIMO (Multi-User Multiple Input, MultipleOutput: MU-MIMO) transmission to the multiple terminals. Alternatively,modes analogous to the first to fourth embodiments are applicable alsoto a communication scheme in which OFDMA and MU-MIMO are combined(called OFDMA & MU-MIMO). In this communication scheme, each of theresource blocks are allocated to multiple terminals, and the downlinkMU-MIMO transmission is performed in units of resource blockssimultaneously in these resource blocks. Combination of the fourthembodiment and any of the first to third embodiments allows a mode forequalizing the opportunities of obtaining access rights on the medium tobe achieved also for this communication scheme.

Fifth Embodiment

FIG. 27 is a functional block diagram of base station (access point) 400according to a fifth embodiment. This access point includescommunication processor 401, transmitter 402, receiver 403, antennas42A, 42B, 42C and 42D, network processor 404, wired I/F 405, and memory406. Access point 400 is connected to server 407 via wired I/F 405.Communication processor 401 has functions analogous to those of MACprocessor 10 and MAC/PHY manager 60 described in the first embodiment.Transmitter 402 and receiver 403 have functions analogous to those ofPHY processor 50 and analog processor 70 described in the firstembodiment. Network processor 404 has a function analogous to that ofupper processor 90 described in the first embodiment. Here,communication processor 401 may internally include a buffer forexchanging data with network processor 404. This buffer may be avolatile memory, such as DRAM, or a nonvolatile memory, such as NAND orMRAM.

Network processor 404 controls data exchange with communicationprocessor 401, reading and writing data from and to memory 406, andcommunication with server 407 via wired I/F 405. Network processor 404may perform a communication process on a layer, such as TCP/IP orUDP/IP, which is the upper layer of the MAC layer, and a process on theapplication layer. The operation of the network processor may beperformed as a process of software (program) by a processor, such asCPU, or performed by hardware or performed by both of software andhardware.

For example, communication processor 401 corresponds to a basebandintegrated circuit, and transmitter 402 and receiver 403 correspond toan RF integrated circuit that transmits and receives frames.Communication processor 401 and network processor 404 may be implementedin one integrated circuit (one chip). A part performing digital domainprocesses of transmitter 402 and receiver 403 and a part performinganalog domain processes thereof may be implemented in different chips.Communication processor 401 may execute a communication process on ahigher layer than the MAC layer; the higher layer may be TCP/IP orUDP/IP. Although the number of antennas is four in this case, it is onlyrequired that at least one antenna is included.

Memory 406 stores therein data received from server 407, and storestherein data received through receiver 402. Memory 406 may be, forexample, a volatile memory, such as DRAM, or a nonvolatile memory, suchas NAND or MRAM. Memory 406 may be an SSD, an HDD, an SD card, an eMMCor the like. Memory 406 may be arranged outside of base station 400.

Wired I/F 405 transmits and receives data to and from server 407. Inthis embodiment, communication with server 407 is performed in a wiredmanner. The communication with server 407 may be executed in a wirelessmanner.

Server 407 is a communication device that returns a response containingrequested data in response to data transfer request for requesting datatransmission. For example, an HTTP server (web server), FTP server orthe like is assumed. However, the implementation is not limited theretoas long as the device includes the function of returning the requesteddata. The device may be a communication device, such as a PC orsmartphone, operated by a user. The device may wirelessly communicatewith base station 400.

When STA belonging to BSS of base station 400 issues a data transferrequest to server 407, a packet pertaining to the data transfer requestis transmitted to base station 400. Base station 400 receives the packetvia antennas 42A to 42D, receiver 403 performs a process on the physicallayer and the like, and communication processor 401 performs a processon the MAC layer and the like.

Network processor 404 analyzes the packet received from communicationprocessor 401. More specifically, the destination ID address, thedestination port number and the like are verified. In a case where thedata in the packet is a data transfer request, such as an HTTP GETrequest, network processor 404 checks whether the data requested by thedata transfer request (e.g., data residing at URL requested in the HTTPGET request) is cashed (stored) in memory 406. Memory 406 stores thereina table that associates URLs (or their archived representation, e.g.,hash values or alternative identifiers) with data. Here, a state wherethe data is cached in memory 406 is represented such that cache dataresides in memory 406.

In a case no cache data resides in memory 406, network processor 404transmits a data transfer request to server 407 via wired I/F 405. Thatis, on behalf of STA, network processor 404 transmits the data transferrequest to server 407. More specifically, network processor 404generates an HTTP request, performs a protocol process, such as adding aTCP/IP header, and passes the packet to wired I/F 405. Wired I/F 405transmits the received packet to server 407.

Wired I/F 405 receives the packet serving as the response to the datatransfer request, from server 407. Network processor 404 grasps that thepacket is destined for STA on the basis of the IP header of the packetreceived via wired I/F 405, and passes the packet to communicationprocessor 401. Communication processor 401 executes a process on the MAClayer for the packet, and transmitter 402 executes a process on thephysical layer therefor, and transmits the packet destined for STA viaantennas 42A to 42D. Here, network processor 404 associates the datareceived from server 407 with the URL (or its archived representation),and stores therein the associated data as cache data in memory 406.

When the cache data resides in memory 406, network processor 404 readsthe data requested by the data transfer request, from memory 406, andtransmits the data to communication processor 401. More specifically, anHTTP header and the like are added to the data read from memory 406, anda protocol process, such as adding a TCP/IP header, is performed, andthe packet is transmitted to communication processor 401. At this time,for example, the transmission source IP address of the packet is set toan IP address identical to the IP address of the server, and thetransmission source port number is set to a port number (the destinationport number of the packet transmitted by the communication terminal)identical to the port number of the server. Consequently, from thestandpoint of STA, communication appears to be made with server 407.Communication processor 401 executes a process on the MAC layer for thepacket, and transmitter 402 executes a process on the physical layertherefor, and transmits the packet destined for STA via antennas 42A to42D.

According to such operations, response is made with frequently accesseddata based on the cache data stored in memory 406, thereby allowing thetraffic between server 407 and base station 400 to be reduced. Theoperation of network processor 404 is not limited to the operation inthis embodiment. No problem occurs with another operation of a typicalor general cache proxy as long as the operation obtains data from server407 instead of STA, caches the data in memory 406, and responds with thecache data in memory 406 in response to a data transfer request for thesame data.

The base station (access point) of this embodiment is applicable as thebase stations of the first to fourth embodiments. For example, the basestation preliminarily receives the data transfer requests issued bymultiple terminals including terminals 1 to 4, and identifies theterminals (here, terminals 1 to 4) in which the data items requested bythe data transfer requests are cashed. The base station reads the datafrom memory 406, generates the data frames containing the respectiveread data items, adds physical headers (a legacy field, preamble 1, andpreambles 2), and downlink-transmits the frames to terminals 1 to 4. Forthe terminal with no data being cached in memory 406, an operation ofobtaining the data requested by server 407 through the data transferrequest and caching the data in memory 406. This operation may beperformed independently of wireless network communication on the sidesof terminals 1 to 4 described before. Here, it is assumed that the datatransmitted to terminals 1 to 4 is the data obtained from server 407.The configuration is not necessarily limited thereto. The data may bedata obtained by any method as long as the data stored in memory 406 istransmitted. For example, the data may be data received from an externaldevice other than server 407. The data cached in memory 406 is notnecessarily transmitted. Alternatively, information based on the cacheddata can be transmitted to terminals in the data frames or managementframes. For example, the information may be information, such as thedata amount or data type of the cached data. In the case of transmissionof this information, a request for transmitting the information may beobtained from the terminal, and the information may be transmitted inresponse to the request. Alternatively, the base station may transmitthe information without receipt of such a request.

The base station may change the length of NAV according to the amount ofdata that is cached in memory 406 and is to be transmitted to terminals1 to 4. In a case where such data is OFDMA-transmitted to terminals 1 to4, it may be configured such that the larger the amount of data is, thelonger the NAV is. For example, the NAV value may be set according tothe largest amount of data. In the example of FIG. 8 , in a case wherethe amounts of data destined for respective terminals 1 to 4 are large,it may be considered that OFDMA transmission of the downlink data frameand OFDMA transmission of the uplink BA frame may be performed multipletimes. In this case, the NAV may be set according to the length ofperiod from the end of the data frame downlink-OFDMA-transmitted first(it is assumed that the ends of data frames of terminals 1 to 4 coincidewith each other in FIG. 8 (including a case of adding padding data)) tothe end of the BA frame uplink-transmitted at the last time of theseries of frames exchanges (the ends of the BA frames transmitted byterminals 1 to 4 coincide with each other in FIG. 8 ). Note that in acase with a TXOP limit, the NAV value is set within the TXOP limit. Inthe simplest case, the TXOP limit is 0 (only one frame can betransmitted). In this case, the NAV value is set up to the end of the BAframe transmitted first. In a case where the TXOP limit is not 0, theNAV value may be set within a limit value according to the data type (ACor TID) and the like. Instead of the configuration that sets the NAVvalue in the Duration field of the header of the MAC frame, aconfiguration may be adopted that sets the value in preamble 1 orpreambles 2 or both of them.

In this embodiment, the base station having the cache function has beendescribed. Alternatively, the same block configuration as that in FIG.27 can achieve a terminal (STA) having the cache function. In this case,wired I/F 405 may be omitted. The terminals of this embodiment may beapplied as the terminals of the first to fourth embodiments. Forexample, terminals 5 and 6 (see FIG. 8 and the like) read the data cachein memory 406 when the access to the wireless medium is not suppressed(after the NAV is canceled in FIG. 8 ), transmit the data framescontaining the read data (more specifically, the physical packet towhich the physical header is added) to the base station. The data may bedata obtained from server 407, or data obtained by another method.Alternatively, data required to generate the acknowledgement responseframe (the BA frame, the ACK frame, etc.) may be read from memory 406,and the acknowledgement response frame may be generated on the basis ofthe data. The data cached in memory 406 is not necessarily transmitted.Alternatively, information based on the cached data can be transmittedto the base station in the data frames, management frames or the like.For example, the information may be information, such as the data amountor data type of the cached data. In the case of transmission of thisinformation, a request for transmitting the information may be obtainedfrom the base station, and the information may be transmitted inresponse to the request. Alternatively, the information may betransmitted without receipt of such a request. In the case of uplinkmulti-user communication (MU-MUMO, OFDMA, etc.), the base station maydetermine the uplink target terminals using the information.Alternatively, the base station may determine terminals that are targetsof downlink multi-user communication, using the information. Forexample, it can be considered that a terminal having at least a certainvalue of data amount, or a terminal having a data amount having at leasta certain ratio to the buffer size is regarded to have a small availablecapacity of the buffer and is not selected as a downlink targetterminal. In a case of multi-hop network, the terminal has both of arole of serving as a terminal as non-base station and a role of servingas a base station. When the terminal operates as a base station, thisterminal is only required to perform the operation of the base stationdescribed before.

Sixth Embodiment

FIG. 28 shows an example of entire configuration of a terminal or a basestation. The example of configuration is just an example, and thepresent embodiment is not limited to this. The terminal or the basestation includes one or a plurality of antennas 1 to n (n is an integerequal to or greater than 1), a wireless LAN module 148, and a hostsystem 149. The wireless LAN module 148 corresponds to the wirelesscommunication device according to the first embodiment. The wireless LANmodule 148 includes a host interface and is connected to the host system149 through the host interface. Other than the connection to the hostsystem 149 through the connection cable, the wireless LAN module 148 maybe directly connected to the host system 149. The wireless LAN module148 can be mounted on a substrate by soldering or the like and can beconnected to the host system 149 through wiring of the substrate. Thehost system 149 uses the wireless LAN module 148 and the antennas 1 to nto communicate with external apparatuses according to an arbitrarycommunication protocol. The communication protocol may include theTCP/IP and a protocol of a layer higher than that. Alternatively, theTCP/IP may be mounted on the wireless LAN module 148, and the hostsystem 149 may execute only a protocol in a layer higher than that. Inthis case, the configuration of the host system 149 can be simplified.Examples of the present terminal include a mobile terminal, a TV, adigital camera, a wearable device, a tablet, a smartphone, a gamedevice, a network storage device, a monitor, a digital audio player, aWeb camera, a video camera, a projector, a navigation system, anexternal adaptor, an internal adaptor, a set top box, a gateway, aprinter server, a mobile access point, a router, an enterprise/serviceprovider access point, a portable device, a hand-held device and so on.

FIG. 29 shows an example of hardware configuration of a WLAN module. Theconfiguration shown in the figure may be applied for each case in wherethe wireless communication device is mounted in non-AP terminal or in AP(Access Point) provided correspondingly to each function. That is, theconfiguration can be applied as specific examples of the wirelesscommunication device in FIG. 1 . In the configuration shown in figure,at least one antenna is included although a plurality of antennas areincluded. In this case, a plurality of sets of a transmission system(216 and 222 to 225), a reception system (217, 232 to 235), a PLL 242, acrystal oscillator (reference signal source) 243, and a switch 245 maybe arranged according to the antennas, and each set may be connected toa control circuit 212. One or both of the PLL 242 and the crystaloscillator 243 correspond to an oscillator according to the presentembodiment.

The wireless LAN module (wireless communication device) includes abaseband IC (Integrated Circuit) 211, an RF (Radio Frequency) IC 221, abalun 225, the switch 245, and the antenna 247.

The baseband IC 211 includes the baseband circuit (control circuit) 212,a memory 213, a host interface 214, a CPU 215, a DAC (Digital to AnalogConverter) 216, and an ADC (Analog to Digital Converter) 217.

The baseband IC 211 and the RF IC 221 may be formed on the samesubstrate. The baseband IC 211 and the RF IC 221 may be formed by onechip. Both or one of the DAC 216 and the ADC 217 may be arranged on theRF IC 221 or may be arranged on another IC. Both or one of the memory213 and the CPU 215 may be arranged on an IC other than the baseband IC.

The memory 213 stores data to be transferred to and from the hostsystem. The memory 213 also stores one or both of information to betransmitted to the terminal or the base station and informationtransmitted from the terminal or the base station. The memory 213 mayalso store a program necessary for the execution of the CPU 215 and maybe used as a work area for the CPU 215 to execute the program. Thememory 213 may be a volatile memory, such as an SRAM or a DRAM, or maybe a non-volatile memory, such as a NAND or an MRAM.

The host interface 214 is an interface for connection to the hostsystem. The interface can be anything, such as UART, SPI, SDIO, USB, orPCI Express.

The CPU 215 is a processor that executes a program to control thebaseband circuit 212. The baseband circuit 212 mainly executes a processof the MAC layer and a process of the physical layer. One or both of thebaseband circuit 212 and the CPU 215 correspond to the communicationcontrol apparatus that controls communication, the controller thatcontrols communication, or controlling circuitry that controlscommunication.

At least one of the baseband circuit 212 or the CPU 215 may include aclock generator that generates a clock and may manage internal time bythe clock generated by the clock generator.

For the process of the physical layer, the baseband circuit 212 performsaddition of the physical header, coding, encryption, modulation process(which may include MIMO modulation), and the like of the frame to betransmitted and generates, for example, two types of digital basebandsignals (hereinafter, “digital I signal” and “digital Q signal”).

The DAC 216 performs DA conversion of signals input from the basebandcircuit 212. More specifically, the DAC 216 converts the digital Isignal to an analog I signal and converts the digital Q signal to ananalog Q signal. Note that a single system signal may be transmittedwithout performing quadrature modulation. When a plurality of antennasare included, and single system or multi-system transmission signalsequivalent to the number of antennas are to be distributed andtransmitted, the number of provided DACs and the like may correspond tothe number of antennas.

The RF IC 221 is, for example, one or both of an RF analog IC and a highfrequency IC. The RF IC 221 includes a filter 222, a mixer 223, apreamplifier (PA) 224, the PLL (Phase Locked Loop) 242, a low noiseamplifier (LNA) 234, a balun 235, a mixer 233, and a filter 232. Some ofthe elements may be arranged on the baseband IC 211 or another IC. Thefilters 222 and 232 may be bandpass filters or low pass filters.

The filter 222 extracts a signal of a desired band from each of theanalog I signal and the analog Q signal input from the DAC 216. The PLL242 uses an oscillation signal input from the crystal oscillator 243 andperforms one or both of division and multiplication of the oscillationsignal to thereby generate a signal at a certain frequency synchronizedwith the phase of the input signal. Note that the PLL 242 includes a VCO(Voltage Controlled Oscillator) and uses the VCO to perform feedbackcontrol based on the oscillation signal input from the crystaloscillator 243 to thereby obtain the signal at the certain frequency.The generated signal at the certain frequency is input to the mixer 223and the mixer 233. The PLL 242 is equivalent to an example of anoscillator that generates a signal at a certain frequency.

The mixer 223 uses the signal at the certain frequency supplied from thePLL 242 to up-convert the analog I signal and the analog Q signal passedthrough the filter 222 into a radio frequency. The preamplifier (PA)amplifies the analog I signal and the analog Q signal at the radiofrequency generated by the mixer 223, up to desired output power. Thebalun 225 is a converter for converting a balanced signal (differentialsignal) to an unbalanced signal (single-ended signal). Although thebalanced signal is handled by the RF IC 221, the unbalanced signal ishandled from the output of the RF IC 221 to the antenna 247. Therefore,the balun 225 performs the signal conversions.

The switch 245 is connected to the balun 225 on the transmission sideduring the transmission and is connected to the LNA 234 or the RF IC 221on the reception side during the reception. The baseband IC 211 or theRF IC 221 may control the switch 245. There may be another circuit thatcontrols the switch 245, and the circuit may control the switch 245.

The analog I signal and the analog Q signal at the radio frequencyamplified by the preamplifier 224 are subjected to balanced-unbalancedconversion by the balun 225 and are then emitted as radio waves to thespace from the antenna 247.

The antenna 247 may be a chip antenna, may be an antenna formed bywiring on a printed circuit board, or may be an antenna formed by usinga linear conductive element.

The LNA 234 in the RF IC 221 amplifies a signal received from theantenna 247 through the switch 245 up to a level that allowsdemodulation, while maintaining the noise low. The balun 235 performsunbalanced-balanced conversion of the signal amplified by the low noiseamplifier (LNA) 234. The mixer 233 uses the signal at the certainfrequency input from the PLL 242 to down-convert, to a baseband, thereception signal converted to a balanced signal by the balun 235. Morespecifically, the mixer 233 includes a unit that generates carrier wavesshifted by a phase of 90 degrees based on the signal at the certainfrequency input from the PLL 242. The mixer 233 uses the carrier wavesshifted by a phase of 90 degrees to perform quadrature demodulation ofthe reception signal converted by the balun 235 and generates an I(In-phase) signal with the same phase as the reception signal and a Q(Quad-phase) signal with the phase delayed by 90 degrees. The filter 232extracts signals with desired frequency components from the I signal andthe Q signal. Gains of the I signal and the Q signal extracted by thefilter 232 are adjusted, and the I signal and the Q signal are outputfrom the RF IC 221.

The ADC 217 in the baseband IC 211 performs AD conversion of the inputsignal from the RF IC 221. More specifically, the ADC 217 converts the Isignal to a digital I signal and converts the Q signal to a digital Qsignal. Note that a single system signal may be received withoutperforming quadrature demodulation.

When a plurality of antennas are provided, the number of provided ADCsmay correspond to the number of antennas. Based on the digital I signaland the digital Q signal, the baseband circuit 212 executes a process ofthe physical layer and the like, such as demodulation process, errorcorrecting code process, and process of physical header, and obtains aframe. The baseband circuit 212 applies a process of the MAC layer tothe frame. Note that the baseband circuit 212 may be configured toexecute a process of TCP/IP when the TCP/IP is implemented.

Seventh Embodiment

FIG. 30A and FIG. 30B are perspective views of wireless terminalaccording to the present embodiment. The wireless terminal in FIG. 30Ais a notebook PC 301 and the wireless communication device (or awireless device) in FIG. 30B is a mobile terminal 321. Each of themcorresponds to one form of a terminal (which may indicate a basestation). The notebook PC 301 and the mobile terminal 321 are equippedwith wireless communication devices 305 and 315, respectively. Thewireless communication device provided in a terminal (which may indicatea base station) which has been described before can be used as thewireless communication devices 305 and 315. A wireless terminal carryinga wireless communication device is not limited to notebook PCs andmobile terminals. For example, it can be installed in a TV, a digitalcamera, a wearable device, a tablet, a smart phone, a gaming device, anetwork storage device, a monitor, a digital audio player, a web camera,a video camera, a projector, a navigation system, an external adapter,an internal adapter, a set top box, a gateway, a printer server, amobile access point, a router, an enterprise/service provider accesspoint, a portable device, a handheld device and so on.

Moreover, a wireless communication device installed in a terminal (whichmay indicate a base station) can also be provided in a memory card. FIG.31 illustrates an example of a wireless communication device mounted ona memory card. A memory card 331 contains a wireless communicationdevice 355 and a body case 332. The memory card 331 uses the wirelesscommunication device 355 for wireless communication with externaldevices. Here, in FIG. 31 , the description of other installed elements(for example, a memory, and so on) in the memory card 331 is omitted.

Eighth Embodiment

In the present embodiment, a bus, a processor unit and an externalinterface unit are provided in addition to the configuration of thewireless communication device according to any of the above embodiments.The processor unit and the external interface unit are connected with anexternal memory (a buffer) through the bus. A firmware operates theprocessor unit. Thus, by adopting a configuration in which the firmwareis included in the wireless communication device, the functions of thewireless communication device can be easily changed by rewriting thefirmware. The processing unit in which the firmware operates may be aprocessor that performs the process of the communication controllingdevice or the control unit according to the present embodiment, or maybe another processor that performs a process relating to extending oraltering the functions of the process of the communication controllingdevice or the control unit. The processing unit in which the firmwareoperates may be included in the access point or the wireless terminalaccording to the present embodiment. Alternatively, the processing unitmay be included in the integrated circuit of the wireless communicationdevice installed in the access point, or in the integrated circuit ofthe wireless communication device installed in the wireless terminal.

Ninth Embodiment

In the present embodiment, a clock generating unit is provided inaddition to the configuration of the wireless communication deviceaccording to any of the above embodiments. The clock generating unitgenerates a clock and outputs the clock from an output terminal to theexterior of the wireless communication device. Thus, by outputting tothe exterior the clock generated inside the wireless communicationdevice and operating the host by the clock output to the exterior, it ispossible to operate the host and the wireless communication device in asynchronized manner.

Tenth Embodiment

In the present embodiment, a power source unit, a power sourcecontrolling unit and a wireless power feeding unit are included inaddition to the configuration of the wireless communication deviceaccording to any of the above embodiments. The power supply controllingunit is connected to the power source unit and to the wireless powerfeeding unit, and performs control to select a power source to besupplied to the wireless communication device. Thus, by adopting aconfiguration in which the power source is included in the wirelesscommunication device, power consumption reduction operations thatcontrol the power source are possible.

Eleventh Embodiment

In the present embodiment, a SIM card is added to the configuration ofthe wireless communication device according to any of the aboveembodiments. For example, the SIM card is connected with MAC processor10, MAC/PHY manager 60, or a controller in the wireless communicationdevice. Thus, by adopting a configuration in which the SIM card isincluded in the wireless communication device, authentication processingcan be easily performed.

Twelfth Embodiment

In the eighth embodiment, a video image compressing/decompressing unitis added to the configuration of the wireless communication deviceaccording to any of the above embodiments. The video imagecompressing/decompressing unit is connected to the bus. Thus, byadopting a configuration in which the video imagecompressing/decompressing unit is included in the wireless communicationdevice, transmitting a compressed video image and decompressing areceived compressed video image can be easily done.

Thirteenth Embodiment

In the present embodiment, an LED unit is added to the configuration ofthe wireless communication device according to any of the aboveembodiments. For example, the LED unit is connected to at least one ofMAC processor 10, MAC/PHY manager 60, a transmission processing circuit,a reception processing circuit or a controller in the wirelesscommunication device. Thus, by adopting a configuration in which the LEDunit is included in the wireless communication device, notifying theoperation state of the wireless communication device to the user can beeasily done.

Fourteenth Embodiment

In the present embodiment, a vibrator unit is included in addition tothe configuration of the wireless communication device wirelesscommunication device according to any of the above embodiments. Forexample, the vibrator unit is connected to at least one of MAC processor10, MAC/PHY manager 60, a transmission processing circuit, a receptionprocessing circuit or a controller in the wireless communication device.Thus, by adopting a configuration in which the vibrator unit is includedin the wireless communication device, notifying the operation state ofthe wireless communication device to the user can be easily done.

Fifteenth Embodiment

In the present embodiment, the configuration of the wirelesscommunication device includes a display in addition to the configurationof the wireless communication device (the wireless communication deviceof the terminal (which may indicate the base station)) according to anyone of the above embodiments. The display may be connected to the MACprocessor in the wireless communication device via a bus (not shown). Asseen from the above, the configuration including the display to displaythe operation state of the wireless communication device on the displayallows the operation status of the wireless communication device to beeasily notified to a user.

Sixteenth Embodiment

In the present embodiment, [1] the frame type in the wirelesscommunication system, [2] a technique of disconnection between wirelesscommunication devices, [3] an access scheme of a wireless LAN system and[4] a frame interval of a wireless LAN are described.

[1] Frame Type in Communication System

Generally, as mentioned above, frames treated on a wireless accessprotocol in a wireless communication system are roughly divided intothree types of the data frame, the management frame and the controlframe. These types are correctly shown in a header part which iscommonly provided to frames. As a display method of the frame type,three types may be distinguished in one field or may be distinguished bya combination of two fields. In IEEE 802.11 standard, identification ofa frame type is made based on two fields of Type and Subtype in theFrame Control field in the header part of the MAC frame. The Type fieldis one for generally classifying frames into a data frame, a managementframe, or a control frame and the Subtype field is one for identifyingmore detailed type in each of the classified frame types such as abeacon frame belonging to the management frame.

The management frame is a frame used to manage a physical communicationlink with a different wireless communication device. For example, thereare a frame used to perform communication setting with the differentwireless communication device or a frame to release communication link(that is, to disconnect the connection), and a frame related to thepower save operation in the wireless communication device.

The data frame is a frame to transmit data generated in the wirelesscommunication device to the different wireless communication deviceafter a physical communication link with the different wirelesscommunication device is established. The data is generated in a higherlayer of the present embodiment and generated by, for example, a user'soperation.

The control frame is a frame used to perform control at the time oftransmission and reception (exchange) of the data frame with thedifferent wireless communication device. A response frame transmittedfor the acknowledgment in a case where the wireless communication devicereceives the data frame or the management frame, belongs to the controlframe. The response frame is, for example, an ACK frame or a BlockACKframe. The RTS frame and the CTS frame are also the control frame.

These three types of frames are subjected to processing based on thenecessity in the physical layer and then transmitted as physical packetsvia an antenna. In IEEE 802.11 standard (including the extended standardsuch as IEEE Std 802.11ac-2013), an association process is defined asone procedure for connection establishment. The association requestframe and the association response frame which are used in the procedureare a management frame. Since the association request frame and theassociation response frame is the management frame transmitted in aunicast scheme, the frames causes the wireless communication terminal inthe receiving side to transmit an ACK frame being a response frame. TheACK frame is a control frame as described in the above.

[2] Technique of Disconnection Between Wireless Communication Devices

For disconnection of the connection (release), there are an explicittechnique and an implicit technique. As the explicit technique, a frameto disconnect any one of the connected wireless communication devices istransmitted. This frame corresponds to Deauthentication frame defined inIEEE 802.11 standard and is classified into the management frame.Correctly, it is determined that the connection is disconnected at thetiming of transmitting the frame to disconnect the connection in awireless communication device on the side to transmit the frame and atthe timing of receiving the frame to disconnect the connection in awireless communication device on the side to receive the frame.Afterward, it returns to the initial state in a communication phase, forexample, a state to search for a wireless communication device of thecommunicating partner. In a case that the wireless communication basestation disconnects with a wireless communication terminal, for example,the base station deletes information on the wireless communicationdevice from a connection management table if the base station holds theconnection management table for managing wireless communicationterminals which entries into the BSS of the base station-self. Forexample, in a case that the base station assigns an AID to each wirelesscommunication terminal which entries into the BSS at the time when thebase station permitted each wireless communication terminal to connectto the base station-self in the association process, the base stationdeletes the held information related to the AID of the wirelesscommunication terminal disconnected with the base station and mayrelease the AID to assign it to another wireless communication devicewhich newly entries into the BSS.

On the other hand, as the implicit technique, it is determined that theconnection state is disconnected in a case where frame transmission(transmission of a data frame and management frame or transmission of aresponse frame with respect to a frame transmitted by the subjectdevice) is not detected from a wireless communication device of theconnection partner which has established the connection for a certainperiod. Such a technique is provided because, in a state where it isdetermined that the connection is disconnected as mentioned above, astate is considered where the physical wireless link cannot be secured,for example, the communication distance to the wireless communicationdevice of the connection destination is separated and the radio signalscannot be received or decoded. That is, it is because the reception ofthe frame to disconnect the connection cannot be expected.

As a specific example to determine the disconnection of connection in animplicit method, a timer is used. For example, at the time oftransmitting a data frame that requests an acknowledgment responseframe, a first timer (for example, a retransmission timer for a dataframe) that limits the retransmission period of the frame is activated,and, if the acknowledgement response frame to the frame is not receiveduntil the expiration of the first timer (that is, until a desiredretransmission period passes), retransmission is performed. When theacknowledgment response frame to the frame is received, the first timeris stopped.

On the other hand, when the acknowledgment response frame is notreceived and the first timer expires, for example, a management frame toconfirm whether a wireless communication device of a connection partneris still present (in a communication range) (in other words, whether awireless link is secured) is transmitted, and, at the same time, asecond timer (for example, a retransmission timer for the managementframe) to limit the retransmission period of the frame is activated.Similarly to the first timer, even in the second timer, retransmissionis performed if an acknowledgment response frame to the frame is notreceived until the second timer expires, and it is determined that theconnection is disconnected when the second timer expires.

Alternatively, a third timer is activated when a frame is received froma wireless communication device of the connection partner, the thirdtimer is stopped every time the frame is newly received from thewireless communication device of the connection partner, and it isactivated from the initial value again. When the third timer expires,similarly to the above, a management frame to confirm whether thewireless communication device of the connection party is still present(in a communication range) (in other words, whether a wireless link issecured) is transmitted, and, at the same time, a second timer (forexample, a retransmission timer for the management frame) to limit theretransmission period of the frame is activated. Even in this case,retransmission is performed if an acknowledgment response frame to theframe is not received until the second timer expires, and it isdetermined that the connection is disconnected when the second timerexpires. The latter management frame to confirm whether the wirelesscommunication device of the connection partner is still present maydiffer from the management frame in the former case. Moreover, regardingthe timer to limit the retransmission of the management frame in thelatter case, although the same one as that in the former case is used asthe second timer, a different timer may be used.

[3] Access Scheme of Wireless LAN System

For example, there is a wireless LAN system with an assumption ofcommunication or competition with a plurality of wireless communicationdevices. CSMA/CA is set as the basis of an access scheme in IEEE802.11(including an extension standard or the like) wireless LAN. In a schemein which transmission by a certain wireless communication device isgrasped and transmission is performed after a fixed time from thetransmission end, simultaneous transmission is performed in theplurality of wireless communication devices that grasp the transmissionby the wireless communication device, and, as a result, radio signalscollide and frame transmission fails. By grasping the transmission bythe certain wireless communication device and waiting for a random timefrom the transmission end, transmission by the plurality of wirelesscommunication devices that grasp the transmission by the wirelesscommunication device stochastically disperses. Therefore, if the numberof wireless communication devices in which the earliest time in a randomtime is subtracted is one, frame transmission by the wirelesscommunication device succeeds and it is possible to prevent framecollision. Since the acquisition of the transmission right based on therandom value becomes impartial between the plurality of wirelesscommunication devices, it can say that a scheme adopting CollisionAvoidance is a suitable scheme to share a radio medium between theplurality of wireless communication devices.

[4] Frame Interval of Wireless LAN

The frame interval of IEEE802.11 wireless LAN is described. There aresix types of frame intervals used in IEEE802.11 wireless LAN, such asdistributed coordination function interframe space (DIFS), arbitrationinterframe space (AIFS), point coordination function interframe space(PIFS), short interframe space (SIFS), extended interframe space (EIFS)and reduced interframe space (RIFS).

The definition of the frame interval is defined as a continuous periodthat should confirm and open the carrier sensing idle beforetransmission in IEEE802.11 wireless LAN, and a strict period from aprevious frame is not discussed. Therefore, the definition is followedin the explanation of IEEE802.11 wireless LAN system. In IEEE802.11wireless LAN, a waiting time at the time of random access based onCSMA/CA is assumed to be the sum of a fixed time and a random time, andit can say that such a definition is made to clarify the fixed time.

DIFS and AIFS are frame intervals used when trying the frame exchangestart in a contention period that competes with other wirelesscommunication devices on the basis of CSMA/CA. DIFS is used in a casewhere priority according to the traffic type is not distinguished, AIFSis used in a case where priority by traffic identifier (TID) isprovided.

Since operation is similar between DIFS and AIFS, an explanation belowwill mainly use AIFS. In IEEE802.11 wireless LAN, access controlincluding the start of frame exchange in the MAC layer is performed. Inaddition, in a case where QoS (Quality of Service) is supported whendata is transferred from a higher layer, the traffic type is notifiedtogether with the data, and the data is classified for the priority atthe time of access on the basis of the traffic type. The class at thetime of this access is referred to as “access category (AC)”. Therefore,the value of AIFS is provided every access category.

PIFS denotes a frame interval to enable access which is morepreferential than other competing wireless communication devices, andthe period is shorter than the values of DIFS and AIFS. SIFS denotes aframe interval which can be used in a case where frame exchangecontinues in a burst manner at the time of transmission of a controlframe of a response system or after the access right is acquired once.EIFS denotes a frame interval caused when frame reception fails (whenthe received frame is determined to be error).

RIFS denotes a frame interval which can be used in a case where aplurality of frames are consecutively transmitted to the same wirelesscommunication device in a burst manner after the access right isacquired once, and a response frame from a wireless communication deviceof the transmission partner is not requested while RIFS is used.

Here, FIG. 32 illustrates one example of frame exchange in a competitiveperiod based on the random access in IEEE802.11 wireless LAN.

When a transmission request of a data frame (W_DATA1) is generated in acertain wireless communication device, a case is assumed where it isrecognized that a medium is busy (busy medium) as a result of carriersensing. In this case, AIFS of a fixed time is set from the time pointat which the carrier sensing becomes idle, and, when a random time(random backoff) is set afterward, data frame W_DATA1 is transmitted tothe communicating partner.

The random time is acquired by multiplying a slot time by a pseudorandominteger led from uniform distribution between contention windows (CW)given by integers from 0. Here, what multiplies CW by the slot time isreferred to as “CW time width”. The initial value of CW is given byCWmin, and the value of CW is increased up to CWmax everyretransmission. Similarly to AIFS, both CWmin and CWmax have valuesevery access category. In a wireless communication device oftransmission destination of W_DATA1, when reception of the data framesucceeds, a response frame (W_ACK1) is transmitted after SIFS from thereception end time point. If it is within a transmission burst timelimit when W_ACK1 is received, the wireless communication device thattransmits W_DATA1 can transmit the next frame (for example, W_DATA2)after SIFS.

Although AIFS, DIFS, PIFS and EIFS are functions between SIFS and theslot-time, SIFS and the slot time are defined every physical layer.Moreover, although parameters whose values being set according to eachaccess category, such as AIFS, CWmin and CWmax, can be set independentlyby a communication group (which is a basic service set (BSS) inIEEE802.11 wireless LAN), the default values are defined.

For example, in the definition of 802.11ac, with an assumption that SIFSis 16 μs and the slot time is 9 μs, and thereby PIFS is 25 μs, DIFS is34 μs, the default value of the frame interval of an access category ofBACKGROUND (AC_BK) in AIFS is 79 μs, the default value of the frameinterval of BEST EFFORT (AC_BE) is 43 μs, the default value of the frameinterval between VIDEO(AC_VI) and VOICE(AC_VO) is 34 μs, and the defaultvalues of CWmin and CWmax are 31 and 1023 in AC_BK and AC_BE, 15 and 31in AC_VI and 7 and 15 in AC_VO. Here, EIFS denotes the sum of SIFS,DIFS, and the time length of a response frame transmitted at the lowestmandatory physical rate. In the wireless communication device which caneffectively takes EIFS, it may estimate an occupation time length of aPHY packet conveying a response frame directed to a PHY packet due towhich the EIFS is caused and calculates a sum of SIFS, DIFS and theestimated time to take the EIFS.

The terms used in each embodiment should be interpreted broadly. Forexample, the term “processor” may encompass a general purpose processor,a central processing unit (CPU), a microprocessor, a digital signalprocessor (DSP), a controller, a microcontroller, a state machine, andso on. According to circumstances, a “processor” may refer to anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), and a programmable logic device (PLD), etc. The term“processor” may refer to a combination of processing devices such as aplurality of microprocessors, a combination of a DSP and amicroprocessor, or one or more microprocessors in conjunction with a DSPcore.

As another example, the term “memory” may encompass any electroniccomponent which can store electronic information. The “memory” may referto various types of media such as a random access memory (RAM), aread-only memory (ROM), a programmable read-only memory (PROM), anerasable programmable read only memory (EPROM), an electrically erasablePROM (EEPROM), a non-volatile random access memory (NVRAM), a flashmemory, and a magnetic or optical data storage, which are readable by aprocessor. It can be said that the memory electronically communicateswith a processor if the processor read and/or write information for thememory. The memory may be arranged within a processor and also in thiscase, it can be said that the memory electronically communication withthe processor.

Note that the frames described in the embodiments may indicate not onlythings called frames in, for example, the IEEE 802.11 standard, but alsothings called packets, such as Null Data Packets.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions.

1. A wireless communication device, comprising a receiver configured toreceive a first field, receive at least one of a plurality of secondfields having been multiplexed and transmitted, and decode the one ofthe second fields to obtain a frame in a case where first informationidentifying the wireless communication device is not set in the firstfield, and a controller configured to suppress access to a wirelessmedium during a period indicated by a value set in the frame.